曼昆英文版《经济学原理》05-弹性及其应用
曼昆《经济学原理(微观经济学分册)》(第6版)课后习题详解(第5章 弹性及其应用)
曼昆《经济学原理（微观经济学分册）》（第6版）第5章 弹性及其应用课后习题详解跨考网独家整理最全经济学考研真题，经济学考研课后习题解析资料库，您可以在这里查阅历年经济学考研真题，经济学考研课后习题，经济学考研参考书等内容，更有跨考考研历年辅导的经济学学哥学姐的经济学考研经验，从前辈中获得的经验对初学者来说是宝贵的财富，这或许能帮你少走弯路，躲开一些陷阱。
以下内容为跨考网独家整理，如您还需更多考研资料，可选择经济学一对一在线咨询进行咨询。
一、概念题1．弹性（elasticity ）答：弹性指作为因变量的经济量的相对变化对作为自变量的经济变量的相对变化的反应程度或灵敏程度。
弹性用来表明两个经济变量变化的关系，当两个经济变量之间存在函数关系时，作为自变量的经济变量的变化，必然引起作为因变量的经济变量的变化。
弹性的大小由弹性系数来表示，弹性系数等于因变量的相对变化对自变量的相对变化的比值。
即：=因变量的变动比例弹性系数自变量的变动比例设两个经济变量之间的函数关系为()Y f X =，则具体的弹性公式为：YY X Y E X X YX∆∆==⋅∆∆ 其中，E 为弹性系数；X ∆、Y ∆分别为变量X 、Y 的变动量。
弹性概念在西方经济学中广泛应用，经济理论中有多种多样的弹性概念，例如，需求价格弹性、需求收入弹性、供给价格弹性等等。
由于弹性是两个量的相对变化的比，因此，弹性是一个具体的数字，它与自变量和因变量的度量单位无关。
2．需求价格弹性（elasticity of demand ）（华南理工大学2009研）答：需求价格弹性指某种商品需求量变动的百分比与价格变动的百分比之比，它用来衡量商品需求量变动对于商品自身价格变动的敏感程度。
用公式表示为：=需求变动的百分比需求价格弹性价格变动的百分比需求价格弹性的经济含义可表示为“当价格变化百分之一时，需求量可能会有百分之几的变化”。
这一概念是由马歇尔在解释价格与需求的关系时提出的。
曼昆微观经济学第5章 弹性及其应用
第5章弹性及其应用内容提要：需求价格弹性衡量的是需求量对价格变量的反应程度。
如果某种物品可以得到相近的替代品，是奢侈品而不是必需品，市场范围狭小，或者买者有相当长的时间对价格变动做出反应，那么，这种物品就倾向于更富有弹性。
可以用需求量变动百分比除以价格变动百分比来计算需求价格弹性。
如果需求量变动比例小于价格变动比例，那么弹性小于1，就可以说需求缺乏弹性。
如果需求量变动比例大于价格变动比例，那么弹性大于1，就可以说需求富有弹性。
总收益，即对一种物品的总支付量，等于该物品的价格乘以销售量。
对于缺乏弹性的需求曲线，其总收益随着价格的上升而增加；对于富有弹性的需求曲线，其总收益随着价格的上升而减少。
需求收入弹性衡量的是需求量对消费者收入变动的反应程度。
需求的交叉价格弹性衡量一种物品需求量对另一种物品价格变动的反应程度。
供给价格弹性衡量的是供给量对价格变动的反应程度。
这种弹性往往取决于所考虑的时间长短。
在大多数市场上，供给在长期中比在短期中更富有弹性。
可以用供给量变动百分比除以价格变动百分比来计算供给价格弹性。
如果供给量变动比例小于价格变动比例，那么弹性小于1，就可以说供给缺乏弹性。
如果供给量变动比例大于价格变动比例，那么弹性大于1，就可以时候供给富有弹性。
供给工具可以被运用于许多不同种类的市场。
小麦市场、石油市场、非法毒品市场。
关键概念：弹性：衡量需求量或供给量对其某种决定因素的反应程度的指标。
富有价格弹性：衡量一种物品需求量对其价格变动反应程度的指标。
用需求量变动百分比除以价格变动百分比来计算。
总收益：一种物品的买者支付从而卖者得到的量，用该物品的价格乘以销售量来计算。
需求收入弹性：衡量一种物品需求量对消费者收入变动反应程度的指标，用需求量变动百分比除以收入变动百分比来计算。
需求的交叉价格弹性：衡量一种物品需求量对另一种物品价格变动的反应程度的指标，用第一种物品需求量变动百分比除以第二种物品价格变动百分比来计算。
《经济学原理》第五章弹性及其应用
《经济学原理》第五章弹性及其应用在本章中你将——了解需求弹性的含义考察决定需求弹性的因素是什么了解供给弹性的含义考察决定供给弹性的因素是什么在三个专门不同的市场上运用弹性的概念上一章中介绍了供给与需求。
在任何一个竞争市场上，例如小麦市场，向右上方倾斜的供给曲线代表卖者的行为，而向右下方倾斜的需求曲线代表买者的行为。
一种物品价格的调整使该物品的需求量与供给量实现平稳。
为了运用这种差不多分析来讲明农业科学家发觉的阻碍，我们必须第一提出另一种工具：弹性的概念。
弹性是衡量买者与卖者对市场条件变动反应大小的指标，它使我们能够更精确地分析供给与需求。
需求弹性需求价格弹性及其决定因素需求规律讲明，一种物品的价格下降使需求量增加。
需求价格弹性衡量需求量对价格变动的反应程度，是一种物品需求量对其价格变动反应程度的衡量，用需求量变动的百分比除以价格变动的百分比来运算。
假如一种物品的需求量对价格变动的反应大，能够讲这种物品的需求是富有弹性的。
假如一种物品的需求量对价格变动的反应小，能够讲这种物品的需求是缺乏弹性的。
什么因素决定一种物品的需求富有弹性依旧缺乏弹性呢? 由于任何一种物品的需求取决于消费者的偏好，因此，需求的价格弹性取决于许多形成个人欲望的经济、社会和心理因素。
然而，依照体会，我们能够讲出某些决定需求价格弹性的一样规律。
必需品与奢侈品必需品倾向于需求缺乏弹性，而奢侈品倾向于需求富有弹性。
当看病的价格上升时，尽管人们会比平常看病的次数少一些，但可不能大幅度地改变他们看病的次数。
与此相比，当游艇价格上升时，游艇需求量会大幅度减少。
缘故是大多数人把看病作为必需品，而把游艇作为奢侈品。
因此，一种物品是必需品依旧奢侈品并不取决于物品本身固有的性质，而取决于买者的偏好。
关于一个热衷于航行而不太关注自己健康的水手来讲，游艇可能是需求缺乏弹性的必需品，而看病是需求富有弹性的奢侈品。
相近替代品的可获得性有相近替代品的物品往往较富有需求弹性，因为消费者从这种物品转向其他物品较为容易。
Chap_05弹性与应用(经济学原理,曼昆,中英文双语)
价格需求弹性的决定因素
需求倾向于富有弹性：
u 如果物品是奢侈品 u 时期更长 u 相近替代品的数量更多 u 市场定义的范围更窄
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
例子: 如果冰激凌蛋卷的价格从2美元上升到 2.2美元,你的购买量从10个下降到8个,你的需求 价格弹性计算如下：
(108) 100 10
(2.202.00) 100
20 10
％ ％
2
2.00
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
Example: If the price of an ice cream cone increases from $2.00 to $2.20 and the amount you buy falls from 10 to 8 cones then your elasticity of demand would be calculated as:
u It is a measure of how much the quantity demanded of a good responds to a change in the price of that good.
Harcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc.
曼昆 经济学原理 第五章 弹性及其应用
第5章弹性及其应用①需求弹性弹性(elasticity)：需求量或供应量对其决定因素的响应程度需求价格弹性(price elasticity of demand)：需求量对价格的响应程度，决定因素如下：1.有相近替代物的商品需求弹性大2.必需品需求弹性小，奢侈品需求弹性大3.市场越狭义(如香草味冰淇淋)弹性越大4.时间跨度越大弹性越大需求价格弹性=需求量的变化百分比/价格变化百分比为避免基准点不同引起不同，常用中值法：需求价格弹性=(Q2-Q1)/[(Q2+Q1)/2](P2-P1)/[(P1+P2)/2]总收益(total revenue)=P×Q需求曲线越平缓弹性越大，曲线竖直为完全无弹性(perfectly elastic)，水平为完全有弹性(perfectly elastic)，需求价格弹性大于1为弹性大(elastic)，价格与总收益成负相关，小于1为弹性小(inelastic)，价格与总收入成正相关，等于1为单位弹性(unit elastic)，总收益不随价格变化线型的需求曲线斜率不变，但弹性随价格升高而增大需求收入弹性(income elasticity of demand)=需求量变化百分比/收入变化百分比需求交叉价格弹性(cross-price elasticity of demand)=a物品需求量变化百分比/b物品价格变化百分比②供应弹性供应价格弹性(price elasticity of supply)：供应量对价格的响应程度，与货物本身属性有关，且时间越长弹性越大供应价格弹性=供应量的变化百分比/价格变化百分比供应曲线越平缓弹性越大，曲线竖直为完全无弹性，水平为完全有弹性，供应价格弹性大于1为弹性大，小于1为弹性小，等于1为单位弹性③应用例1：小麦的需求弹性小，增产的新技术使小麦供应增大，均衡价格降低，麦农更贫穷例2：OPEC减产以提高价格，短期内石油弹性小，价格高，长期上其他国家加大开发石油力度、消费者改用节能品，供应增加需求减少，价格回落例3：毒品禁令使毒品供应减少，但由于需求弹性小，用于毒品的总金额增大，导致更多犯罪，而毒品教育使毒品需求降低，均衡价格和数量均降低。
经济学原理5
点弹性：需求曲线上两点之间的变化量趋于无 穷小时的弹性。令ΔP趋于0，某点及邻近范围 的弹性，是某点需求量无穷小变动率对价格无 穷小变动率的反应程度。
Lou,Fang School of Economics,SHUFE
计算需求价格弹性
需求价格弹性
需求量变动的百分比 价格变动的百分比
例1: 如果冰激凌蛋卷的价格从2美元上升到2.2 美元，你的购买量从10个下降到8个，你的需 求价格弹性计算如下：
如果需求曲线上的A、B两点价格分别为5和4 ，相应需求量分别为400和800，当价格由5 降为4时，或者当商品的价格由4上升至5时， 应该如何计算相应的弧弹性值呢？
Lou,Fang School of Economics,SHUFE
由A点到B点和由B点到A点的弧弹性数值不同 。
因为：尽管ΔQ和ΔP的绝对值都相等，但由于 P和Q所取的基数值不同，两种计算结果便不 同。
Price 价格
1. A 22% $5 increase i1n.价pr格ice上... 升4 22％…
Demand 需求
80
100
Quantity 数量
2. ...leads to a 22%Loud,Feacngrease in quantity. Sch2o…ol o.f使Eco需nom求ics量,SHU减FE少22％。
如果需求富有弹性，价格上升引起总收益减少。因 为价格上升引起需求量减少的比例大。
Total Revenue and the Price Elasticity of Demand
总收益与需求价格弹性
Price 价格
$4
P x Q = $400 P (total revenue 总收益)
曼昆_经济学原理答案_英文版chp5
Chapter 5Elasticity and its applicationSolutions to text problemsprice elasticity of demand. Explain the relationship between total QZ Definerevenue and the price elasticity of demand. (page 92)The price elasticity of demand is a measure of how much the quantity demanded of a good responds to a change in the price of that good, calculated as the percentage change in quantity demanded divided by the percentage change in price.The relationship between total revenue and the price elasticity of demand is: (1) when a demand curve is inelastic (a price elasticity less than 1), a price increase raises total revenue, and a price decrease reduces total revenue; (2) when a demand curve is elastic (a price elasticity greater than 1), a price increase reduces total revenue, and a price decrease raises total revenue; and (3) when a demand curve is unit elastic (a price elasticity equal to 1), a change in price does not affect total revenue.price elasticity of supply. Explain why the price elasticity of supply QZ Definemight be different in the long run than in the short run. (page 94)The price elasticity of supply is a measure of how much the quantity supplied of a good responds to a change in the price of that good, calculated as the percentage change in quantity supplied divided by the percentage change in price.The price elasticity of supply might be different in the long run than in the short run because over short periods of time, firms cannot easily change the size of their factories to make more or less of a good. Thus, in the short run, the quantity supplied is not very responsive to the price. However, over longer periods, firms can build new factories or close old ones, or they can enter or exit a market. So, in the long run, the quantity supplied can respond substantially to the price.QZ How might a drought that destroys half of all farm crops be good for farmers? If such a drought is good for farmers, why don’t farmers destroy their own crops in the absence of a drought? (page 100)A drought that destroys half of all farm crops could be good for farmers if the demand for the crops is inelastic. The shift to the left of the supply curve leads to a price increase that raises total revenue because the price elasticity is less than one.Even though a drought could be good for farmers, they wouldn’t destroy their crops in the absence of a drought because no one farmer would have an incentive to destroy her crops, since she takes the market price as given. Only if all farmers destroyed their crops together, for example through a government program, would this plan work to make farmers better off.Questions for review (page 101)1The price elasticity of demand measures how much the quantity demanded responds to a change in price. The income elasticity of demand measures how much the quantity demanded changes as consumer income changes.2The determinants of the price elasticity of demand include whether the good is a necessity or a luxury, how available close substitutes are, how broadly defined the market is, and the time horizon.Luxury goods have greater price elasticity than necessities, goods with close substitutes have greater elasticity, goods in more narrowly defined markets have greater elasticity, and goods have greater elasticity the longer the time horizon.3Elasticity greater than 1 means demand is elastic. When the elasticity is greater than 1, the percentage change in quantity demanded exceeds the percentage change in price. When the elasticity60 Principles of Economics, Third edition, Instructor’s Manualequals 0, demand is perfectly inelastic. There is no change in quantity demanded when there is a change in price.4Figure 5.1 presents a supply-and-demand diagram, showing equilibrium price, equilibrium quantity, total spending by consumers and the total revenue received by producers. Total spending byconsumers equals the equilibrium price times the equilibrium quantity. Total revenue received by producers also equals the equilibrium price times the equilibrium quantity. These are shown by the area of the rectangle in Figure 5.1.Figure 5.15If demand is elastic, an increase in price reduces total revenue. With elastic demand, the quantity demanded falls by a greater percentage than the percentage increase in price. As a result, total revenue declines.6 A good with an income elasticity less than 0 is called an inferior good because as income rises, thequantity demanded declines.Chapter 5: Elasticity and its application 61 7The price elasticity of supply is calculated as the percentage change in quantity supplied divided by percentage change in price.Price elasticity of supply =% change in quantity supplied % change in priceIt measures how much the quantity supplied responds to changes in the price.8The price elasticity of supply of Picasso paintings is zero, since no matter how high price rises, no more can ever be produced.9The price elasticity of supply is usually larger in the long run than it is in the short run. Over short periods of time, firms cannot easily change the size of their factories to make more or less of a good, so the quantity supplied is not very responsive to price. Over longer periods, firms can build new factories or close old ones, so the quantity supplied is more responsive to price.10OPEC was unable to maintain a high price through the 1980s because the elasticity of supply and demand were more elastic in the long run. When the price of oil rose, producers of oil outside of OPEC increased oil exploration and built new extraction capacity. Consumers responded withgreater conservation efforts. As a result, supply increased and demand fell, leading to a lower price for oil in the long run.Problems and applications (page 102)1 a Mystery novels have more elastic demand than required textbooks, because mystery novels haveclose substitutes and are more of a luxury good, while required textbooks are more of a necessity with no close substitutes. If the price of mystery novels were to rise, readers could substituteother types of novels, or buy fewer novels altogether. But if the price of required textbooks were to rise, students would have little choice but to pay the higher price. Thus the quantity demanded of required textbooks is less responsive to price than the quantity demanded of mystery novels.b Beethoven recordings have more elastic demand than classical music recordings in general.Beethoven recordings are a narrower market than classical music recordings, so it is easy to find close substitutes for them. If the price of Beethoven recordings were to rise, people couldsubstitute other classical recordings, like Mozart. But if the price of all classical recordings were to rise, substitution would be more difficult. A transition from classical music to hip-hop, forexample, is less likely. Thus the quantity demanded of classical recordings is less responsive to price than the quantity demanded of Beethoven recordings.c Heating oil during the next 5 years has more elastic demand than heating oil during the next 6months. Goods have a more elastic demand over longer time horizons. If the price of heating oil were to rise temporarily, consumers couldn’t switch to other sources of fuel without greatexpense. But if the price of heating oil were to be high for a long time, people would gradually switch to gas or electric heat. As a result, the quantity demanded of heating oil during the next 6 months is less responsive to price than the quantity demanded of heating oil during the next 5years.d Lemonade has more elastic demand than water. Lemonade is a luxury with close substitutes,while water is a necessity with no close substitutes. If the price of water were to rise, consumers have little choice but to pay the higher price. But if the price of lemonade were to rise,consumers could easily switch to other soft drinks. So the quantity demanded of lemonade ismore responsive to price than the quantity demanded of water.2 a(i) For business travellers, the price elasticity of demand when the price of tickets risesfrom $200 to $250 is [(2,000 – 1,900)/1,950]/[(250 – 200)/225] = 3/13 = 0.23.(ii) For holiday-makers, the price elasticity of demand when the price of tickets risesfrom $200 to $250 is [(800 – 600)/700] / [(250 – 200)/225] = 9/7 = 1.29.b The price elasticity of demand for holiday-makers is higher than the elasticity for businesstravellers because holiday-makers can more easily choose a different mode of transportation like driving or taking the train. Business travellers are less likely to do so since time is moreimportant to them and their schedules are less adaptable.62 Principles of Economics, Third edition, Instructor’s Manual3 a(i) If your income is $10,000, your price elasticity of demand as the price of compactdiscs rises from $8 to $10 is [(40 – 32)/36] / [(10 – 8)/9] = 1(ii) If your income is $12,000, the elasticity is [(50 – 45)/47.5] / [(10 – 8)/9] = 9/19 =0.47b(i) If the price is $12, your income elasticity of demand as your income increases from $10,000 to $12,000 is [(30 – 24)/27] / [(12,000 – 10,000)/11,000] = 11/9 = 1.22.(ii) If the price is $16, your income elasticity of demand as your income increases from $10,000 to $12,000 is [(12 – 8)/10] / [(12,000 – 10,000)/11,000] = 11/5 = 2.2.4 a If Emily always spends one-third of her income on clothing, then her income elasticityof demand is one, since maintaining her clothing expenditures as a constant fraction ofher income means the percentage change in her quantity of clothing must equal herpercentage change in income. For example, suppose the price of clothing is $30, herincome is $9,000, and she purchases 100 clothing items. If her income rose 10 percentto $9,900, she’d spend a total of $3,300 on clothing, which is 110 clothing items, a 10percent increase.b Emily’s price elasticity of clothing demand is also one, since every percentage point increase inthe price of clothing would lead her to reduce her quantity purchased by the same percentage.Again, suppose the price of clothing is $30, her income is $9,000, and she purchases 100clothing items. If the price of clothing rose 1 percent to $30.30, she would purchase 99 clothing items, a 1 percent reduction. Note this part of the problem can be confusing to students if theyhave an example with a larger percentage change and they use the point elasticity calculationmethod. This example can be used to further illustrate the usefulness of the midpoint method for any size change.c Since Emily spends a smaller proportion of her income on clothing, then for any given price, herquantity demanded will be lower. Thus her demand curve has shifted to the left. But becauseshe’ll again spend a constant fraction of her income on clothing, her income and price elasticities of demand remain one.5 a With a 4.3 percent decline in quantity following a 20 percent increase in price, theprice elasticity of demand is only 4.3/20 = 0.215, which is fairly inelastic.b With inelastic demand, the revenue rises when the fare rises.c The elasticity estimate might be unreliable because it’s only the first month after the fareincrease. As time goes by, people may switch to other means of transportation in response to the price increase. So the elasticity may be larger in the long run than it is in the short run.6Tom’s price elasticity of demand is zero, since he wants the same quantity regardless of the price.Jerry’s price elasticity of demand is one, since he spends the same amount on gas, no matter what the price, which means his percentage change in quantity is equal to the percentage change in price.7To explain the observation that spending on restaurant meals declines more during economic downturns than does spending on food to be eaten at home, economists look at the income elasticity of demand. In economic downturns, people have lower income. To explain the observation, the income elasticity of restaurant meals must be larger than the income elasticity of spending on food to be eaten at home.8 a With a price elasticity of demand of 0.4, reducing the quantity demanded of cigarettes by 20percent requires a 50 percent increase in price, since 20/50 = 0.4. With the price of a pack ofcigarettes currently at $8, this would require an increase in the price to $13.33 a pack using the midpoint method (note that ($13.33 – $8)/$10.67 = 0.50).b The policy will have a larger effect five years from now than it does one year from now. Theelasticity is larger in the long run, since it may take some time for people to reduce theircigarette usage. The habit of smoking is hard to break in the short run.c Since teenagers don’t have as much income as adults, they are likely to have a higher priceelasticity of demand.9You’d expect the price elasticity of demand to be higher in the market for vanilla ice cream than for all ice cream because vanilla ice cream is a narrower category and other flavours of ice cream are almost perfect substitutes for vanilla.Chapter 5: Elasticity and its application 63 You’d expect the price elasticity of supply to be larger for vanilla ice cream than for all ice cream. A producer of vanilla ice cream could easily adjust the quantity of vanilla ice cream and produce other types of ice cream. But a producer of ice cream would have a more difficult time adjusting the overall quantity of ice cream they produced.10 a As Figure 5.2 shows, in both markets, the increase in supply reduces the equilibrium price andincreases the equilibrium quantity.b In the market for pharmaceutical drugs, with inelastic demand, the increase in supply leads to arelatively large decline in the price and not much of an increase in quantity. This marketexperiences a larger change in price.Figure 5.2c In the market for computers, with elastic demand, the increase in supply leads to a relativelylarge increase in quantity and not much of a decline in price. This market experiences a largerchange in quantity.d In the market for pharmaceutical drugs, since demand is inelastic, the percentage increase inquantity will be less than the percentage decrease in price, so total consumer spending willdecline. In contrast, since demand is elastic in the market for computers, the percentage increase in quantity will be greater than the percentage decrease in price, so total consumer spending will increase.11 a As Figure 5.3 shows, in both markets, the increase in demand increases both the equilibriumprice and the equilibrium quantity.b In the market for beachfront resorts, with inelastic supply, the increase in demand leads to arelatively large increase in the price and not much of an increase in quantity. This marketexperiences a larger change in price.c In the market for cars, with elastic supply, the increase in demand leads to a relatively largeincrease in quantity and not much of an increase in price. This market experiences a largerchange in quantity.d In both markets, total consumer spending rises, since both equilibrium price and equilibriumquantity rise.64 Principles of Economics, Third edition, Instructor’s Manual Figure 5.3Quantity of cars 12 a Vineyard owners whose vines weren’t destroyed benefited because the destruction of some ofthe vines reduced the supply, causing the equilibrium price to rise.b To tell whether vineyard owners as a group were hurt or helped by the floods, you’d need toknow the price elasticity of demand. It could be that the additional income earned by vineyard owners whose vines weren’t destroyed rose more because of the higher prices than the lossesmade by vineyard owners whose vines were destroyed, if demand is inelastic.13 A worldwide drought could increase the total revenue of farmers if the price elasticity of demand forgrain is inelastic. The drought reduces the supply of grain, but if demand is inelastic, the reduction of supply causes a large increase in price. Total farm revenue would rise as a result. If there’s only a drought in Queensland, Queensland’s production isn’t a large enough proportion of the total farm product to have much impact on the price. As a result, price is basically unchanged, while the output of Queensland farmers declines, thus reducing their income.14 When productivity increases for all farmland at a point in time, the increased productivity leads to arise in farmland prices, since more output can be produced on a given amount of land. But prior to the technological improvements, the productivity of farmland depended mainly on the prevailing weather conditions. There was little opportunity to substitute land with worse weather conditions for land with better weather conditions. As technology improved over time, it became much easier to substitute one type of land for another. So the price elasticity of supply for farmland increased over time, since now land with bad weather is a better substitute for land with good weather. Theincreased supply of land reduced farmland prices. As a result, productivity and farmland prices are negatively related over time.15 Not necessarily. If demand for luxury cars is price elastic, then raising the price of luxury cars byincreasing the tax will decrease the total revenue from luxury cars. It is likely that demand for luxury cars is elastic as they are more of a luxury than a necessity. P r i c e o f c a r s。
曼昆-微观经济学-第五章-弹性及其应用
弹性
▪ 基本想法：
弹性衡量一种变量对另一种变量反应程度的指标
▪ 一种弹性衡量如果你提高价格，对你网站的需
求会下降多少?
▪ 定义:
弹性衡量需求量或供给量对其某种决定因素的反 应程度的指标
弹性及其应用
3
需求价格弹性
需求价格弹性 =
需求量变动百分比 价格变动百分比
▪ 需求价格弹性衡量一种物品需求量对其价格变动
弹性及其应用
18
各种需求曲线
▪ 需求价格弹性与需求曲线的斜率密切相关
▪ 拇指规则：
通过某一点的需求曲线越平坦，需求的价格弹性 就越大 通过某一点的需求曲线越陡峭，需求的价格弹性 就越小
▪ 需求曲线的五种不同分类.…
弹性及其应用
19
“完全无弹性的需求” (一个极端例子)
需求价格弹性 = 需求量变动百分比 =
▪ 数量的变动百分比等于：
12 – 8 x 100% = 40.0% 10
▪ 需求的价格弹性等于:
40/22.2 = 1.8
弹性及其应用
10
主动学习 1
计算弹性
利用下述数据计算宾馆 房间的需求价格弹性： 如果 P = $70， Qd = 5000 如果 P = $90， Qd = 3000
11
主动学习 1
29
总收益与需求价格弹性
现在，需求是缺乏 弹性的：
弹性 = 0.82
如果 P = $200, Q = 12 ，
收益 = $2400 如果P = $250, Q = 10 ， 收益 = $2500
P
$250 $200
价格对上你升的所网站的 增加的收需益求 需求量
减少所 损失的 收益
D
曼昆《经济学原理》第6版微观经济学分册第5章课后习题答案解析P113_P
第五章弹性及其应用复习题1 •给需求价格弹性和需求收入弹性下定义。
答：需求价格弹性，是指一种物品需求量对其价格变动反应程度的衡量；需求收入弹性，是指一种物品需求量对消费者收入变动反应程度的衡量。
2 •列出并解释本章中所谈论的决定需求价格弹性的四个因素。
答：需求的价格弹性取决于许多形成个人欲望的经济、社会和心理因素。
通常，需求价格弹性主要由以下几个因素决定：（1）相似替代品的可获得性。
有相似替代品的物品往往富有需求弹性，因为消费者从这种物品转向其他物品较为容易。
（2）必需品与奢侈品。
必需品倾向于需求缺乏弹性，奢侈品倾向于需求富有弹性。
（3）市场的定义。
范围小的市场的需求弹性往大于范围大的市场，因为范围小的市场上的物品更容易找到相近的替代品。
（4）时间框架。
物品往往随着时间变长而需求更富有弹性，因为在长期中人们有充分的时间来改变自己的消费嗜好和消费结构。
4 •如果弹性大于1 ,需求是富有弹性还是缺乏弹性？如果弹性等于零，需求是完全有弹性还是完全无弹性？答：弹性大于1 ,需求富有弹性。
弹性等于零，需求完全无弹性。
5 •在一个供求图上标明均衡价格、均衡数量和生产者得到的总收益。
答：如图，供给与需求曲线的交点是均衡点，均衡点所对应的价格P是均衡价格，所对应的数量Q是均衡数量。
PQ,即阴影部分是生产者得到的总收益。
6 •如果需求是富有弹性的，价格上升会如何改变总收益？解释原因。
答：如果需求是富有弹性的，价格上升会使总收益减少。
因为需求富有弹性，价格上升引起需求量减少的如此之多，以至于大到抵消价格上涨所带来的收益，即需求量下降的比例大于价格上升的比例。
7 •如果一种物品需求收入弹性小于零，我们把这种物品称为什么？答：需求收入弹性小于零的物品，我们称为低档物品。
8•如何计算供给的价格弹性？供给价格弹性衡量什么？答：供给价格弹性=供给量变动的百分比/价格变动百分比。
它是衡量供给量对其价格变动的反应程度。
9 .毕加索油画的供给价格弹性是多大？答：毕加索油画的供给价格弹性为零。
曼昆经济学原理第五章
弹性分类
完全缺乏弹性（Perfectly
Inelastic） Elastic）
需求量对价格变化没有反应
完全富有弹性（Perfectly
需求量对价格变化反应强烈
单位弹性（Unit
Elastic）
需求量变动与价格变动幅度一致
需求曲线的多样性
正是由于需求弹性的不同， 导致价格变化引起需求量变 化存在差异，从而引起需求 曲线有时平缓有时陡峭。
弹性应用
考察是供给曲线移动还是需求曲线移动 考虑曲线向哪个方向移动
用供求图说明市场均衡如何变动
.
小麦市场供给增加
小麦价格
S1
$3
D
0 100 小麦数量
小麦市场供给增加
小麦价格
1. 当需求曲线缺乏弹性时， 供给增加...
S1
S2
2. …导致 $3 更大的 2 价格 下降...
D 0 100 110 小麦数量
需求弹性与总收益: 富有弹性
价格
价格从 $4上升到 $5...
价格
…总收益从$200下降 到 $100
$5 $4
总收益 = $200
D
D
总收益 = $100
0
50
需求量
0
20
需求量
线性需求曲线的弹性计算
总收益 (PxQ) $0 12 20 24 24 20 12 0 需求量变动百 分比 15% 18 22 29 40 67 200
需求弹性与总收益: 缺乏弹性
价格 价格
价格从$1 上升到 $3...
…导致总收益从$100 上升到 $240
$3 总收益 = $240 $1 总收益 = $100
经济学原理第五章课后题答案
第五章弹性及其应用复习题：1、给需求价格弹性和需求收入弹性下定义。
答：需求价格弹性，是指一种物品需求量对其价格变动反应程度的衡量；需求收入弹性，是指一种物品需求量对消费者收入变动反应程度的衡量。
2、列出并解释决定需求价格弹性的一些因素。
答：需求价格弹性取决于许多形成个人欲望的经济、社会和心理因素。
通常，需求价格弹性主要有以下几个因素决定：①必需品与奢侈品。
必需品倾向于需求缺乏弹性，奢侈品倾向于需求富有弹性。
②相似替代品的可获得性。
有相似替代品的物品往往富有需求弹性，因为消费者从这种物品转向其他物品较为容易。
③市场的定义。
范围小的市场的需求弹性往往大于范围大的市场，因为范围小的市场上的物品更容易找到相近的替代品。
④时间的长短。
物品往往随着时间的变长而需求更富有弹性，因为在长期中人们有充分的时间来改变自己的消费嗜好和消费结构。
3、如果弹性大于1，需求是富有弹性还是缺乏弹性？如果弹性等于0，需求是完全有弹性还是完全无弹性？答：弹性大于1，需求富有弹性。
弹性等于0，需求完全无弹性。
4、根据供求图说明均衡价格、均衡数量和生产者得到的总收益。
答：如图，供求与需求曲线的交点是均衡点，均衡点所对应的价格P 是均衡价格，所对应的数量Q是均衡数量。
P*Q，即红色部分是生产者得到的总收益。
5、如果需求是富有弹性的，价格上升会如何改变总收益呢？解释原因。
答：如果需求是富有弹性的，价格上升会使总收益减少。
因为需求富有弹性，价格上升引起需求量减少的如此之多，以至于大到抵消价格上升所带来的收益，即需求量下降的比例大于价格上升的比例。
6、如果一种物品需求收入弹性小于0，我们把这种物品称为什么？ 答：需求收入弹性小于0的物品，我们称为低档物品。
7、如何计算供给的价格弹性？解释这个公式衡量什么？答：供给价格弹性=供给量变动的百分比/价格变动百分比。
他是衡量供给量对其价格变动的反应程度。
8、毕加索油画的供给价格弹性是多大？答：毕加索油画的供给价格弹性为零。
曼昆经济学原理英文版文案加习题答案5章ELASTICITY AND ITS APPLICATION
5ELASTICITY AND ITS APPLICATION WHAT’S NEW IN THE S EVENTH EDITION:There are no major changes to this chapter.LEARNING OBJECTIVES:By the end of this chapter, students should understand:the meaning of the elasticity of demand.what determines the elasticity of demand.the meaning of the elasticity of supply.what determines the elasticity of supply.the concept of elasticity in three very different markets (the market for wheat, the market for oil, and the market for illegal drugs).CONTEXT AND PURPOSE:Chapter 5 is the second chapter of a three-chapter sequence that deals with supply and demand and how markets work. Chapter 4 introduced supply and demand. Chapter 5 shows how much buyersand sellers respond to changes in market conditions. Chapter 6 will address the impact of government polices on competitive markets.The purpose of Chapter 5 is to add precision to the supply-and-demand model. We introduce the concept of elasticity, which measures the responsiveness of buyers and sellers to changes in economic variables such as prices and income. The concept of elasticity allows us to make quantitative observations about the impact of changes in supply and demand on equilibrium prices and quantities.KEY POINTS:The price elasticity of demand measures how much the quantity demanded responds to changes in the price. Demand tends to be more elastic if close substitutes are available, if the good is a luxury rather than a necessity, if the market is narrowly defined, or if buyers have substantial time to react to a price change.The price elasticity of demand is calculated as the percentage change in quantity demanded divided by the percentage change in price. If quantity demanded moves proportionately less than the price, then the elasticity is less than one, and demand is said to be inelastic.If quantity demanded moves proportionately more than the price, then the elasticity is greater than one, and demand is said to be elastic.Total revenue, the total amount paid for a good, equals the price of the good times the quantity sold. For inelastic demand curves, total revenue moves in the same direction as the price. For elastic demand curves, total revenue moves in the opposite direction as the price.The income elasticity of demand measures how much the quantity demanded responds tochanges in consumers’ income. The cross-price elasticity of demand measures how much the quantity demanded of one good responds to the price of another good.The price elasticity of supply measures how much the quantity supplied responds to changes in the price. This elasticity often depends on the time horizon under consideration. In most markets, supply is more elastic in the long run than in the short run.The price elasticity of supply is calculated as the percentage change in quantity supplied divided by the percentage change in price. If quantity supplied moves proportionately less than the price, then the elasticity is less than one, and supply is said to be inelastic.If quantity supplied moves proportionately more than the price, then the elasticity is greater than one, and supply is said to be elastic.The tools of supply and demand can be applied in many different kinds of markets. This chapter uses them to analyze the market for wheat, the market for oil, and the market for illegal drugs.CHAPTER OUTLINE:I. The Elasticity of DemandA. Definition of elasticity: a measure of the responsiveness of quantity demanded orquantity supplied to one of its determinants.B. The Price Elasticity of Demand and Its Determinants1. Definition of price elasticity of demand: a measure of how much the quantitydemanded of a good responds to a change in the price of that good, computed as thepercentage change in quantity demanded divided by the percentage change in price.2. Determinants of the Price Elasticity of Demanda. Availability of Close Substitutes: the more substitutes a good has, the moreelastic its demand.b. Necessities versus Luxuries: necessities are more price inelastic.c. Definition of the market: narrowly defined markets (ice cream) have moreelastic demand than broadly defined markets (food).d. Time Horizon: goods tend to have more elastic demand over longer time horizons.C. Computing the Price Elasticity of Demand1. Formula2. Example: the price of ice cream rises by 10% and quantity demanded falls by 20%.Price elasticity of demand = (20%)/(10%) = 23. Because there is an inverse relationship between price and quantity demanded (theprice of ice cream rose by 10% and the quantity demanded fell by 20%), the price elasticity of demand is sometimes reported as a negative number. We will ignorethe minus sign and concentrate on the absolute value of the elasticity.D. The Midpoint Method: A Better Way to Calculate Percentage Changes and Elasticities1. Because we use percentage changes in calculating the price elasticity of demand,the elasticity calculated by going from one point to another on a demand curvewill be different from an elasticity calculated by going from the second point tothe first. This difference arises because the percentage changes are calculatedusing a different base.a. A way around this problem is to use the midpoint method.b. Using the midpoint method involves calculating the percentage change in eitherprice or quantity demanded by dividing the change in the variable by themidpoint between the initial and final levels rather than by the initial levelitself.c. Example: the price rises from $4 to $6 and quantity demanded falls from 120 to80.% change in price = (6 −4)/5 × 100 = 40%% change in quantity demanded = (120 − 80)/100 x 100 = 40%price elasticity of demand = 40/40 = 1E. The Variety of Demand Curves1. Classification of Elasticitya. When the price elasticity of demand is greater than one, demand is defined tobe elastic.b. When the price elasticity of demand is less than one, the demand is defined tobe inelastic.c. When the price elasticity of demand is equal to one, the demand is said to haveunit elasticity.2. In general, the flatter the demand curve that passes through a given point, themore elastic the demand.3. Extreme Casesa. When the price elasticity of demand is equal to zero, the demand is perfectlyinelastic and is a vertical line.b. When the price elasticity of demand is infinite, the demand is perfectlyelastic and is a horizontal line.4. FYI: A Few Elasticities from the Real WorldF. Total Revenue and the Price Elasticity of Demand1. Definition of total revenue: the amount paid by buyers and received by sellers ofa good, computed as the price of the good times the quantity sold.2. If demand is inelastic, the percentage change in price will be greater than thepercentage change in quantity demanded.a. If price rises, quantity demanded falls, and total revenue will rise (becausethe increase in price will be larger than the decrease in quantity demanded).b. If price falls, quantity demanded rises, and total revenue will fall (becausethe fall in price will be larger than the increase in quantity demanded).3. If demand is elastic, the percentage change in quantity demanded will be greaterthan the percentage change in price.a. If price rises, quantity demanded falls, and total revenue will fall (becausethe increase in price will be smaller than the decrease in quantity demanded).b. If price falls, quantity demanded rises, and total revenue will rise (becausethe fall in price will be smaller than the increase in quantity demanded).4. If demand is unit elastic, the percentage change in price will be equal to thepercentage change in quantity demanded.a. If price rises, quantity demanded falls, and total revenue will remain the same(because the increase in price will be equal to the decrease in quantitydemanded).b. If price falls, quantity demanded rises, and total revenue will remain the same(because the fall in price will be equal to the increase in quantity demanded).G. Elasticity and Total Revenue along a Linear Demand Curve1. The slope of a linear demand curve is constant, but the elasticity is not.a. At points with a low price and a high quantity demanded, demand is inelastic.b. At points with a high price and a low quantity demanded, demand is elastic.2. Total revenue also varies at each point along the demand curve.H. Other Demand Elasticities1. Definition of income elasticity of demand: a measure of how much the quantitydemanded of a good responds to a change in consumers’ income, computed as the percentage change in quantity demanded divided by the percentage change in income.a. FormulaFigure 4Note that when demand is elastic and price falls, total revenue rises. Also point out that once demand is inelastic, any further decrease in price% change in quantity demandedIncome elasticity of demand =% change in incomeb. Normal goods have positive income elasticities, while inferior goods havenegative income elasticities.ALTERNATIVE CLASSROOM EXAMPLE:John’s income rises from $20,000 to $22,000 and the quantity of hamburger he buyseach week falls from 2 pounds to 1 pound.% change in quantity demanded = (1−2)/ x 100 = %% change in income = (22,000 −20,000)/21,000 x 100 = %c. Necessities tend to have small income elasticities, while luxuries tend to havelarge income elasticities.2. Definition of cross-price elasticity of demand: a measure of how much the quantitydemanded of one good responds to a change in the price of another good, computedas the percentage change in the quantity demanded of the first good divided by the percentage change in the price of the second good.a. Formulab. Substitutes have positive cross-price elasticities, while complements havenegative cross-price elasticities.ALTERNATIVE CLASSROOM EXAMPLE:The price of apples rises from $ per pound to $ per pound. As a result, thequantity of oranges demanded rises from 8,000 per week to 9,500.% change in quantity of oranges demanded = (9,500 − 8,000)/8,750 x 100 = %% change in price of apples = − / x 100 = 40%II. The Elasticity of SupplyA. The Price Elasticity of Supply and Its Determinants1. Definition of price elasticity of supply: a measure of how much the quantitysupplied of a good responds to a change in the price of that good, computed as thepercentage change in quantity supplied divided by the percentage change in price.2. Determinants of the Price Elasticity of Supplya. Flexibility of sellers: goods that are somewhat fixed in supply (beachfrontproperty) have inelastic supplies.b. Time horizon: supply is usually more inelastic in the short run than in thelong run.B. Computing the Price Elasticity of Supply1. Formula2. Example: the price of milk increases from $ per gallon to $ per gallon and thequantity supplied rises from 9,000 to 11,000 gallons per month.% change in price = –/ × 100 = 10%% change in quantity supplied = (11,000 –9,000)/10,000 × 100 = 20%Price elasticity of supply = (20%)/(10%) = 2C. The Variety of Supply Curves1. In general, the flatter the supply curve that passes through a given point, themore elastic the supply.2. Extreme Casesa. When the elasticity is equal to zero, the supply is said to be perfectlyinelastic and is a vertical line.b. When the elasticity is infinite, the supply is said to be perfectly elastic andis a horizontal line.3. Because firms often have a maximum capacity for production, the elasticity ofsupply may be very high at low levels of quantity supplied and very low at highlevels of quantity supplied.III. Three Applications of Supply, Demand, and ElasticityA. Can Good News for Farming Be Bad News for Farmers1. A new hybrid of wheat is developed that is more productive than those used in thepast. What happens2. Supply increases, price falls, and quantity demanded rises.3. If demand is inelastic, the fall in price is greater than the increase in quantitydemanded and total revenue falls.4. If demand is elastic, the fall in price is smaller than the rise in quantitydemanded and total revenue rises.5. In practice, the demand for basic foodstuffs (like wheat) is usually inelastic.a. This means less revenue for farmers.b. Because farmers are price takers, they still have the incentive to adopt thenew hybrid so that they can produce and sell more wheat.c. This may help explain why the number of farms has declined so dramatically overthe past two centuries.d. This may also explain why some government policies encourage farmers todecrease the amount of crops planted.B. Why Did OPEC Fail to Keep the Price of Oil HighFigure 8Short Run Long Run1. In the 1970s and 1980s, OPEC reduced the amount of oil it was willing to supply toworld markets. The decrease in supply led to an increase in the price of oil and a decrease in quantity demanded. The increase in price was much larger in the short run than the long run. Why2. The demand and supply of oil are much more inelastic in the short run than thelong run. The demand is more elastic in the long run because consumers can adjust to the higher price of oil by carpooling or buying a vehicle that gets bettermileage. The supply is more elastic in the long run because non-OPEC producerswill respond to the higher price of oil by producing more.C. Does Drug Interdiction Increase or Decrease Drug-Related Crime1. The federal government increases the number of federal agents devoted to the waron drugs. What happensa. The supply of drugs decreases, which raises the price and leads to a reductionin quantity demanded. If demand is inelastic, total expenditure on drugs (equalto total revenue) will increase. If demand is elastic, total expenditure willfall.b. Thus, because the demand for drugs is likely to be inelastic, drug-relatedcrime may rise.2. What happens if the government instead pursued a policy of drug educationa. The demand for drugs decreases, which lowers price and quantity supplied. Totalexpenditure must fall (because both price and quantity fall).b. Thus, drug education should not increase drug-related crime.SOLUTIONS TO TEXT PROBLEMS:Quick Quizzes1. The price elasticity of demand is a measure of how much the quantity demanded of agood responds to a change in the price of that good, computed as the percentage change in quantity demanded divided by the percentage change in price.When demand is inelastic (a price elasticity less than 1), a price increase raisestotal revenue, and a price decrease reduces total revenue. When demand is elastic (a price elasticity greater than 1), a price increase reduces total revenue, and a price decrease increases total revenue. When demand is unit elastic (a price elasticity equal to 1), a change in price does not affect total revenue.2. The price elasticity of supply is a measure of how much the quantity supplied of agood responds to a change in the price of that good, computed as the percentage change in quantity supplied divided by the percentage change in price.The price elasticity of supply might be different in the long run than in theshort run because over short periods of time, firms cannot easily change the sizes Figure 9(a) Drug Interdiction (b) Drug Educationof their factories to make more or less of a good. Thus, in the short run, thequantity supplied is not very responsive to the price. However, over longerperiods, firms can build new factories, expand existing factories, close oldfactories, or they can enter or exit a market. So, in the long run, the quantitysupplied can respond substantially to a change in price.3. A drought that destroys half of all farm crops could be good for farmers (at leastthose unaffected by the drought) if the demand for the crops is inelastic. Theshift to the left of the supply curve leads to a price increase that will raisetotal revenue if the price elasticity of demand is less than 1.No one farmer would have an incentive to destroy her crops in the absence of adrought because she takes the market price as given. Only if all farmersdestroyed a portion of their crops together, for example through a governmentprogram, would this plan work to make farmers better off.Questions for Review1. The price elasticity of demand measures how much quantity demanded responds to achange in price. The income elasticity of demand measures how much quantitydemanded responds to changes in consumers' income.2. The determinants of the price elasticity of demand include the availability ofclose substitutes, whether the good is a necessity or a luxury, the breadth of thedefinition of the market, and the time horizon. Goods with close substitutes havegreater elasticities, luxury goods have greater price elasticities thannecessities, goods in more narrowly defined markets have greater elasticities, andthe elasticity of demand is greater the longer the time horizon.3. An elasticity greater than one means that demand is elastic. When the elasticityis greater than one, the percentage change in quantity demanded exceeds thepercentage change in price. When the elasticity equals zero, demand is perfectly inelastic. There is no change in quantity demanded when there is a change in price.4. Figure 1 presents a supply-and-demand diagram, showing the equilibrium price, P,the equilibrium quantity, Q, and the total revenue received by producers. Total revenue equals the equilibrium price times the equilibrium quantity, which is the area of the rectangle shown in the figure.Figure 15. If demand is elastic, an increase in price reduces total revenue. With elasticdemand, the quantity demanded falls by a greater percentage than the price rises.As a result, total revenue moves in the opposite direction as the price. Thus, if price rises, total revenue falls.6. A good with income elasticity less than zero is called an inferior good because asincome rises, the quantity demanded declines.7. The price elasticity of supply is calculated as the percentage change in quantitysupplied divided by the percentage change in price. It measures how much quantity supplied responds to changes in price.8. If a fixed quantity of a good is available and no more can be made, the priceelasticity of supply is zero. Regardless of the percentage change in price, therewill be no change in the quantity supplied.9. Destruction of half of the fava bean crop is more likely to hurt fava bean farmersif the demand for fava beans is very elastic. Destruction of half of the cropcauses the supply curve to shift to the left resulting in a higher price of favabeans. When demand is very elastic, an increase in price leads to a decrease intotal revenue because the decrease in quantity demanded outweighs the increase inprice.Quick Check Multiple Choice1. a2. b3. d4. c5. a6. cProblems and Applications1. a. Mystery novels have more elastic demand than required textbooks because mysterynovels have close substitutes and are a luxury good, while required textbooksare a necessity with no close substitutes. If the price of mystery novels wereto rise, readers could substitute other types of novels, or buy fewer novelsaltogether. But if the price of required textbooks were to rise, students wouldhave little choice but to pay the higher price. Thus, the quantity demanded ofrequired textbooks is less responsive to price than the quantity demanded ofmystery novels.b. Beethoven recordings have more elastic demand than classical music recordingsin general. Beethoven recordings are a narrower market than classical musicrecordings, so it is easier to find close substitutes for them. If the price of Beethoven recordings were to rise, people could substitute other classicalrecordings, like Mozart. But if the price of all classical recordings were torise, substitution would be more difficult. (A transition from classical musicto rap is unlikely!) Thus, the quantity demanded of classical recordings isless responsive to price than the quantity demanded of Beethoven recordings.c. Subway rides during the next five years have more elastic demand than subwayrides during the next six months. Goods have a more elastic demand over longertime horizons. If the fare for a subway ride was to rise temporarily, consumers could not switch to other forms of transportation without great expense orgreat inconvenience. But if the fare for a subway ride was to remain high for a long time, people would gradually switch to alternative forms of transportation.As a result, the quantity demanded of subway rides during the next six monthswill be less responsive to changes in the price than the quantity demanded ofsubway rides during the next five years.d. Root beer has more elastic demand than water. Root beer is a luxury with closesubstitutes, while water is a necessity with no close substitutes. If the price of water were to rise, consumers have little choice but to pay the higher price.But if the price of root beer were to rise, consumers could easily switch toother sodas or beverages. So the quantity demanded of root beer is moreresponsive to changes in price than the quantity demanded of water.2. a. For business travelers, the price elasticity of demand when the price oftickets rises from $200 to $250 is [(2,000 – 1,900)/1,950]/[(250 – 200)/225]= = . For vacationers, the price elasticity of demand when the price oftickets rises from $200 to $250 is [(800 – 600)/700] / [(250 – 200)/225] == .b. The price elasticity of demand for vacationers is higher than the elasticityfor business travelers because vacationers can choose a substitute more easilythan business travelers. For example, vacationers can choose a different mode of transportation (like driving or taking the train), a different destination, a different departure date, and a different return date. They may also choose to not travel at all. Business travelers are less likely to do so because their schedules are less adaptable.3. a. The percentage change in price is equal to – / x 100 = 20%. If the priceelasticity of demand is , quantity demanded will fall by 4% in the short run [ ]. If the price elasticity of demand is , quantity demanded will fall by 14% in the long run [].b. Over time, consumers can make adjustments to their homes by purchasingalternative heat sources such as natural gas or electric furnaces. Thus, they can respond more easily to the change in the price of heating oil in the long run than in the short run.4. If quantity demanded fell, price must have increased according to the law ofdemand. For a price increase to increase total revenue, the percentage increase in the price must be greater than the percentage decline in quantity demanded. Therefore, demand is inelastic.5. , a. The effect on the market for coffee beans is shown in Figure 2. When ahurricane destroys half of the crop, the supply of coffee beans decreases, the price of coffee beans increases, and the quantity decreases.QuantityPrice Figure 2Demand S 1 S 2b. The effect on the market for cups of coffee is shown in Figure 2. When theprice of coffee beans, an important input into the production of a cup ofcoffee, increases, the supply of cups of coffee decreases, the price of a cup of coffee increases, and the quantity decreases.Because cups of coffee have an inelastic demand, when the price of a cup ofcoffee increases, the total expenditure on coffee increases.c. The effect on the market for donuts is shown in Figure 3. When the price ofcoffee increases and the quantity demanded of coffee decreases, consumersdemand fewer donuts because coffee and donuts are complements. When demanddecreases, the price of donuts decreases.Because donuts have an inelastic demand, when the price of donuts decreases,the total expenditure on donuts decreases.6. a. If your income is $10,000, your price elasticity of demand as the price of DVDsrises from $8 to $10 is [(40 – 32)/36]/[(10 – 8)/9] = = 1. If your income is $12,000, the elasticity is [(50 – 45)/]/[(10 – 8)/9] = = .b. If the price is $12, your income elasticity of demand as your income increasesfrom $10,000 to $12,000 is [(30 – 24)/27]/[(12,000 – 10,000)/11,000] = = . Price Figure 3If the price is $16, your income elasticity of demand as your income increases from $10,000 to $12,000 is [(12 – 8)/10]/[(12,000 – 10,000)/11,000] = = .7. a. If Maria always spends one-third of her income on clothing, then her incomeelasticity of clothing demand is one, because maintaining her clothingexpenditures as a constant fraction of her income means the percentage changein her quantity of clothing must equal her percentage change in income.b. Maria's price elasticity of clothing demand is also one, because everypercentage point increase in the price of clothing would lead her to reduce her quantity purchased by the same percentage.c. Because Maria spends a smaller proportion of her income on clothing, then forany given price, her quantity demanded will be lower. Thus, her demand curvehas shifted to the left. Because she will again spend a constant fraction ofher income on clothing, her income and price elasticities of demand remain one.8. a. The percentage change in price (using the midpoint formula) is – / × 100%= %. Therefore, the price elasticity of demand is = , which is very elastic.b. Because the demand is inelastic, the Transit Authority's revenue rises when thefare rises.c. The elasticity estimate might be unreliable because it is only the first monthafter the fare increase. As time goes by, people may switch to other means oftransportation in response to the price increase. So the elasticity may belarger in the long run than it is in the short run.9. Walt's price elasticity of demand is zero, because he wants the same quantityregardless of the price. Jessie's price elasticity of demand is one, because he spends the same amount on gas, no matter what the price, which means hispercentage change in quantity is equal to the percentage change in price.10. a. With a price elasticity of demand of , reducing the quantity demanded ofcigarettes by 20% requires a 50% increase in price, because 20/50 = . With the price of cigarettes currently $2, this would require an increase in the priceto $ a pack using the midpoint method (note that ($ – $2)/$ = .50).b. The policy will have a larger effect five years from now than it does one yearfrom now. The elasticity is larger in the long run, because it may take sometime for people to reduce their cigarette usage. The habit of smoking is hardto break in the short run.c. Because teenagers do not have as much income as adults, they are likely to havea higher price elasticity of demand. Also, adults are more likely to beaddicted to cigarettes, making it more difficult to reduce their quantitydemanded in response to a higher price.11. To determine whether you should increase or decrease the price of admissions, youneed to know if the demand is elastic or inelastic. If demand is elastic, adecline in the price of admissions will increase total revenue. If demand isinelastic, an increase in the price of admissions will cause total revenue to rise.12. A worldwide drought could increase the total revenue of farmers if the priceelasticity of demand for grain is inelastic. The drought reduces the supply of grain, but if demand is inelastic, the reduction of supply causes a large increase in price. Total farm revenue would rise as a result. If there is only a drought in Kansas, Kansas’ production is not a large enough proportion of the total farm product to have much impact on the price. As a result, price does not change (or changes by only a slight amount), while the output by Kansas farmers declines, thus reducing their income.。
曼昆经济学原理第五版答案(第1-3篇)
第1篇导言第1章经济学十大原理问题与应用1．描写下列每种情况所面临的权衡取舍：A．一个家庭决定是否买一辆新车。
答：如果买新车就要减少家庭其他方面的开支，如：外出旅行，购置新家具；如果不买新车就享受不到驾驶新车外出的方便和舒适。
B．国会议员决定对国家公园支出多少。
答：对国家公园的支出数额大，国家公园的条件可以得到改善，环境会得到更好的保护。
但同时，政府可用于交通、邮电等其他公共事业的支出就会减少。
C．一个公司总裁决定是否新开一家工厂。
答：开一家新厂可以扩大企业规模，生产更多的产品。
但可能用于企业研发的资金就少了。
这样，企业开发新产品、利用新技术的进度可能会减慢。
D．一个教授决定用多少时间备课。
答：教授若将大部分时间用于自己研究，可能会出更多成果，但备课时间减少影响学生授课质量。
E．一个刚大学毕业的学生决定是否去读研究生。
答：毕业后参加工作，可即刻获取工资收入；但继续读研究生，能接受更多知识和未来更高收益。
2．你正想决定是否去度假。
度假的大部分成本((机票、旅馆、放弃的工资))都用美元来衡量，但度假的收益是心理的。
你将如何比较收益与成本呢??答：这种心理上的收益可以用是否达到既定目标来衡量。
对于这个行动前就会作出的既定目标，我们一定有一个为实现目标而愿意承担的成本范围。
在这个可以承受的成本范围内，度假如果满足了既定目标，如：放松身心、恢复体力等等，那么，就可以说这次度假的收益至少不小于它的成本。
3．你正计划用星期六去从事业余工作，但一个朋友请你去滑雪。
去滑雪的真实成本是什么？现在假设你已计划这天在图书馆学习，这种情况下去滑雪的成本是什么？请解释之。
答：去滑雪的真实成本是周六打工所能赚到的工资，我本可以利用这段时间去工作。
如果我本计划这天在图书馆学习，那么去滑雪的成本是在这段时间里我可以获得的知识。
4．你在篮球比赛的赌注中赢了100美元。
你可以选择现在花掉它或在利率为55%的银行中存一年。
现在花掉100美元的机会成本是什么呢?答：现在花掉100 美元的机会成本是在一年后得到105 美元的银行支付(利息+本金)。
曼昆《经济学原理(微观经济学分册)》笔记和课后习题(含考研真题)详解-弹性及其应用【圣才出品】
第5章弹性及其应用5.1复习笔记1．需求价格弹性（1）需求价格弹性的含义与公式需求价格弹性指衡量某种物品需求量的相对变动对于价格的相对变动的敏感程度。
用公式表示为：一般用中点法计算（P1，Q1）和（P2，Q2）两点间的需求价格弹性，公式为：分子是用中点法计算的数量变动百分比，分母是用中点法计算的价格变动百分比。
（2）影响需求价格弹性的因素①相近替代品的可获得性有相近替代品的物品往往富有需求弹性，因为消费者从这种物品转向其他物品较为容易。
②必需品与奢侈品必需品需求倾向于缺乏弹性，而奢侈品需求倾向于富有弹性。
③市场的定义范围小的市场的需求弹性往往大于范围大的市场，因为范围小的市场上的物品更容易找到相近的替代品。
④时间范围一般说来，物品的需求往往在长期内更富有弹性。
（3）需求曲线与需求价格弹性的关系由于需求的价格弹性衡量需求量对价格的反应程度，所以，它与需求曲线的斜率密切相关：通过某一点的需求曲线越平坦，需求的价格弹性就越大；通过某一点的需求曲线越陡峭，需求的价格弹性就越小。
图5-1表示不同需求价格弹性下的需求曲线形状。
图5-1需求曲线与需求价格弹性的关系（4）总收益与需求价格弹性总收益指厂商按照一定价格出售一定量产品所获得的全部收入，等于该产品的价格乘以销售量。
需求价格弹性小于1时，总收益和价格同方向变动；需求价格弹性大于1时，总收益和价格反方向变动；需求价格弹性正好等于1时，总收益是固定的，不随价格变化而变化。
2．需求收入弹性需求收入弹性衡量某种物品需求量的相对变动对于消费者收入的相对变动的敏感程度。
用公式表示为：需求收入弹性大于零的物品为正常物品，正常物品的需求量随收入水平的增加而增加；需求收入弹性小于零的物品为低档物品，低档物品的需求量随收入水平的增加而减少。
3．需求交叉价格弹性需求交叉价格弹性衡量某种商品需求量的相对变动对于另一种商品价格的相对变动的敏感程度。
用公式表示为：需求交叉价格弹性是正数，则物品1和物品2是替代关系；需求交叉价格弹性是负数，则物品1和物品2是互补关系；需求交叉价格弹性等于零，则物品1和物品2没有关系。
曼昆经济学原理英文版文案加习题答案5章elasticityanditsapplication
5ELASTICITY AND ITS APPLICATION WHAT’S NEW IN THE S EVENTH EDITION:There are no major changes to this chapter.LEARNING OBJECTIVES:By the end of this chapter, students should understand:the meaning of the elasticity of demand.what determines the elasticity of demand.the meaning of the elasticity of supply.what determines the elasticity of supply.the concept of elasticity in three very different markets (the market for wheat, the market for oil, and the market for illegal drugs).CONTEXT AND PURPOSE:Chapter 5 is the second chapter of a three-chapter sequence that deals with supply and demand and how markets work. Chapter 4 introduced supply and demand. Chapter 5 shows how much buyers and sellers respond to changes in market conditions. Chapter 6 will address the impact of government polices on competitive markets.The purpose of Chapter 5 is to add precision to the supply-and-demand model. We introduce the concept of elasticity, which measures the responsiveness of buyers and sellers to changes in economic variables such as prices and income. The concept of elasticity allows us to make quantitative observations about the impact of changes in supply and demand on equilibrium prices and quantities.KEY POINTS:The price elasticity of demand measures how much the quantity demanded responds to changes in the price. Demand tends to be more elastic if close substitutes are available, if the good is a luxury rather than a necessity, if the market is narrowly defined, or if buyers have substantial time to react to a price change.The price elasticity of demand is calculated as the percentage change in quantity demanded divided by the percentage change in price. If quantity demanded moves proportionately less than the price, then the elasticity is less than one, and demand is said to be inelastic.If quantity demanded moves proportionately more than the price, then the elasticity is greater than one, and demand is said to be elastic.Total revenue, the total amount paid for a good, equals the price of the good times the quantity sold. For inelastic demand curves, total revenue moves in the same direction as the price. For elastic demand curves, total revenue moves in the opposite direction as the price.The income elasticity of demand measures how much the quantity demanded responds tochanges in consumers’ income. The cross-price elasticity of demand measures how much the quantity demanded of one good responds to the price of another good.The price elasticity of supply measures how much the quantity supplied responds to changes in the price. This elasticity often depends on the time horizon under consideration. In most markets, supply is more elastic in the long run than in the short run.The price elasticity of supply is calculated as the percentage change in quantity supplied divided by the percentage change in price. If quantity supplied moves proportionately less than the price, then the elasticity is less than one, and supply is said to be inelastic.If quantity supplied moves proportionately more than the price, then the elasticity is greater than one, and supply is said to be elastic.The tools of supply and demand can be applied in many different kinds of markets. This chapter uses them to analyze the market for wheat, the market for oil, and the market for illegal drugs.CHAPTER OUTLINE:I. The Elasticity of DemandA. Definition of elasticity: a measure of the responsiveness of quantity demanded orquantity supplied to one of its determinants.B. The Price Elasticity of Demand and Its Determinants1. Definition of price elasticity of demand: a measure of how much the quantitydemanded of a good responds to a change in the price of that good, computed as thepercentage change in quantity demanded divided by the percentage change in price.2. Determinants of the Price Elasticity of Demanda. Availability of Close Substitutes: the more substitutes a good has, the moreelastic its demand.b. Necessities versus Luxuries: necessities are more price inelastic.c. Definition of the market: narrowly defined markets (ice cream) have moreelastic demand than broadly defined markets (food).d. Time Horizon: goods tend to have more elastic demand over longer time horizons.C. Computing the Price Elasticity of Demand1. Formula2. Example: the price of ice cream rises by 10% and quantity demanded falls by 20%.Price elasticity of demand = (20%)/(10%) = 23. Because there is an inverse relationship between price and quantity demanded (theprice of ice cream rose by 10% and the quantity demanded fell by 20%), the price elasticity of demand is sometimes reported as a negative number. We will ignorethe minus sign and concentrate on the absolute value of the elasticity.D. The Midpoint Method: A Better Way to Calculate Percentage Changes and Elasticities1. Because we use percentage changes in calculating the price elasticity of demand,the elasticity calculated by going from one point to another on a demand curvewill be different from an elasticity calculated by going from the second point to the first. This difference arises because the percentage changes are calculatedusing a different base.a. A way around this problem is to use the midpoint method.b. Using the midpoint method involves calculating the percentage change in eitherprice or quantity demanded by dividing the change in the variable by themidpoint between the initial and final levels rather than by the initial levelitself.c. Example: the price rises from $4 to $6 and quantity demanded falls from 120 to80.% change in price = (6 −4)/5 × 100 = 40%% change in quantity demanded = (120 − 80)/100 x 100 = 40%price elasticity of demand = 40/40 = 1E. The Variety of Demand Curves1. Classification of Elasticitya. When the price elasticity of demand is greater than one, demand is defined tobe elastic.b. When the price elasticity of demand is less than one, the demand is defined tobe inelastic.c. When the price elasticity of demand is equal to one, the demand is said to haveunit elasticity.2. In general, the flatter the demand curve that passes through a given point, themore elastic the demand.3. Extreme Casesa. When the price elasticity of demand is equal to zero, the demand is perfectlyinelastic and is a vertical line.b. When the price elasticity of demand is infinite, the demand is perfectlyelastic and is a horizontal line.4. FYI: A Few Elasticities from the Real WorldF. Total Revenue and the Price Elasticity of Demand1. Definition of total revenue: the amount paid by buyers and received by sellers ofa good, computed as the price of the good times the quantity sold.2. If demand is inelastic, the percentage change in price will be greater than thepercentage change in quantity demanded.a. If price rises, quantity demanded falls, and total revenue will rise (becausethe increase in price will be larger than the decrease in quantity demanded).b. If price falls, quantity demanded rises, and total revenue will fall (becausethe fall in price will be larger than the increase in quantity demanded).3. If demand is elastic, the percentage change in quantity demanded will be greaterthan the percentage change in price.a. If price rises, quantity demanded falls, and total revenue will fall (becausethe increase in price will be smaller than the decrease in quantity demanded).b. If price falls, quantity demanded rises, and total revenue will rise (becausethe fall in price will be smaller than the increase in quantity demanded).4. If demand is unit elastic, the percentage change in price will be equal to thepercentage change in quantity demanded.a. If price rises, quantity demanded falls, and total revenue will remain the same(because the increase in price will be equal to the decrease in quantitydemanded).b. If price falls, quantity demanded rises, and total revenue will remain the same(because the fall in price will be equal to the increase in quantity demanded).G. Elasticity and Total Revenue along a Linear Demand Curve1. The slope of a linear demand curve is constant, but the elasticity is not.a. At points with a low price and a high quantity demanded, demand is inelastic.b. At points with a high price and a low quantity demanded, demand is elastic.2. Total revenue also varies at each point along the demand curve.H. Other Demand Elasticities1. Definition of income elasticity of demand: a measure of how much the quantitydemanded of a good responds to a change in consumers’ income, computed as the percentage change in quantity demanded divided by the percentage change in income.a. Formulab. Normal goods have positive income elasticities, while inferior goods havenegative income elasticities.Figure 4Note that when demand is elastic and price falls, total revenue rises. Also point out that once demand is inelastic, any further decrease in price results in a decrease in total revenue.% change in quantity demandedIncome elasticity of demand =% change in incomeALTERNATIVE CLASSROOM EXAMPLE:John’s income rises from $20,000 to $22,000 and the quantity of hamburger he buyseach week falls from 2 pounds to 1 pound.% change in quantity demanded = (1−2)/ x 100 = %% change in income = (22,000 −20,000)/21,000 x 100 = %income elasticity = %/% =Point out that hamburger is an inferior good for John.c. Necessities tend to have small income elasticities, while luxuries tend to havelarge income elasticities.2. Definition of cross-price elasticity of demand: a measure of how much the quantitydemanded of one good responds to a change in the price of another good, computedas the percentage change in the quantity demanded of the first good divided by the percentage change in the price of the second good.a. Formulab. Substitutes have positive cross-price elasticities, while complements havenegative cross-price elasticities.ALTERNATIVE CLASSROOM EXAMPLE:The price of apples rises from $ per pound to $ per pound. As a result, thequantity of oranges demanded rises from 8,000 per week to 9,500.% change in quantity of oranges demanded = (9,500 − 8,000)/8,750 x 100 = %% change in price of apples = − / x 100 = 40%cross-price elasticity = %/40% =Because the cross-price elasticity is positive, the two goods are substitutes.II. The Elasticity of SupplyA. The Price Elasticity of Supply and Its Determinants1. Definition of price elasticity of supply: a measure of how much the quantitysupplied of a good responds to a change in the price of that good, computed as thepercentage change in quantity supplied divided by the percentage change in price.2. Determinants of the Price Elasticity of Supplya. Flexibility of sellers: goods that are somewhat fixed in supply (beachfrontproperty) have inelastic supplies.b. Time horizon: supply is usually more inelastic in the short run than in thelong run.B. Computing the Price Elasticity of Supply1. Formula2. Example: the price of milk increases from $ per gallon to $ per gallon and thequantity supplied rises from 9,000 to 11,000 gallons per month.% change in price = –/ × 100 = 10%% change in quantity supplied = (11,000 –9,000)/10,000 × 100 = 20%Price elasticity of supply = (20%)/(10%) = 2C. The Variety of Supply Curves1. In general, the flatter the supply curve that passes through a given point, themore elastic the supply.2. Extreme Casesa. When the elasticity is equal to zero, the supply is said to be perfectlyinelastic and is a vertical line.b. When the elasticity is infinite, the supply is said to be perfectly elastic andis a horizontal line.3. Because firms often have a maximum capacity for production, the elasticity ofsupply may be very high at low levels of quantity supplied and very low at highlevels of quantity supplied.III. Three Applications of Supply, Demand, and ElasticityA. Can Good News for Farming Be Bad News for Farmers1. A new hybrid of wheat is developed that is more productive than those used in thepast. What happens2. Supply increases, price falls, and quantity demanded rises.3. If demand is inelastic, the fall in price is greater than the increase in quantitydemanded and total revenue falls.4. If demand is elastic, the fall in price is smaller than the rise in quantitydemanded and total revenue rises.5. In practice, the demand for basic foodstuffs (like wheat) is usually inelastic.a. This means less revenue for farmers.b. Because farmers are price takers, they still have the incentive to adopt thenew hybrid so that they can produce and sell more wheat.c. This may help explain why the number of farms has declined so dramatically overthe past two centuries.d. This may also explain why some government policies encourage farmers todecrease the amount of crops planted.B. Why Did OPEC Fail to Keep the Price of Oil HighFigure 8Short Run Long Run1. In the 1970s and 1980s, OPEC reduced the amount of oil it was willing to supply toworld markets. The decrease in supply led to an increase in the price of oil and a decrease in quantity demanded. The increase in price was much larger in the short run than the long run. Why2. The demand and supply of oil are much more inelastic in the short run than thelong run. The demand is more elastic in the long run because consumers can adjust to the higher price of oil by carpooling or buying a vehicle that gets bettermileage. The supply is more elastic in the long run because non-OPEC producerswill respond to the higher price of oil by producing more.C. Does Drug Interdiction Increase or Decrease Drug-Related Crime1. The federal government increases the number of federal agents devoted to the waron drugs. What happensa. The supply of drugs decreases, which raises the price and leads to a reductionin quantity demanded. If demand is inelastic, total expenditure on drugs (equalto total revenue) will increase. If demand is elastic, total expenditure willfall.b. Thus, because the demand for drugs is likely to be inelastic, drug-relatedcrime may rise.2. What happens if the government instead pursued a policy of drug educationa. The demand for drugs decreases, which lowers price and quantity supplied. Totalexpenditure must fall (because both price and quantity fall).b. Thus, drug education should not increase drug-related crime.SOLUTIONS TO TEXT PROBLEMS:Quick Quizzes1. The price elasticity of demand is a measure of how much the quantity demanded of agood responds to a change in the price of that good, computed as the percentage change in quantity demanded divided by the percentage change in price.When demand is inelastic (a price elasticity less than 1), a price increase raisestotal revenue, and a price decrease reduces total revenue. When demand is elastic (a price elasticity greater than 1), a price increase reduces total revenue, and a price decrease increases total revenue. When demand is unit elastic (a price elasticity equal to 1), a change in price does not affect total revenue.2. The price elasticity of supply is a measure of how much the quantity supplied of agood responds to a change in the price of that good, computed as the percentage change in quantity supplied divided by the percentage change in price.The price elasticity of supply might be different in the long run than in theshort run because over short periods of time, firms cannot easily change the sizes of their factories to make more or less of a good. Thus, in the short run, the quantity supplied is not very responsive to the price. However, over longer periods, firms can build new factories, expand existing factories, close old factories, or they can enter or exit a market. So, in the long run, the quantity supplied can respond substantially to a change in price.3. A drought that destroys half of all farm crops could be good for farmers (at leastthose unaffected by the drought) if the demand for the crops is inelastic. The shift to the left of the supply curve leads to a price increase that will raise total revenue if the price elasticity of demand is less than 1.Figure 9(a) Drug Interdiction (b) Drug EducationNo one farmer would have an incentive to destroy her crops in the absence of adrought because she takes the market price as given. Only if all farmersdestroyed a portion of their crops together, for example through a governmentprogram, would this plan work to make farmers better off.Questions for Review1. The price elasticity of demand measures how much quantity demanded responds to achange in price. The income elasticity of demand measures how much quantitydemanded responds to changes in consumers' income.2. The determinants of the price elasticity of demand include the availability ofclose substitutes, whether the good is a necessity or a luxury, the breadth of thedefinition of the market, and the time horizon. Goods with close substitutes havegreater elasticities, luxury goods have greater price elasticities thannecessities, goods in more narrowly defined markets have greater elasticities, andthe elasticity of demand is greater the longer the time horizon.3. An elasticity greater than one means that demand is elastic. When the elasticityis greater than one, the percentage change in quantity demanded exceeds thepercentage change in price. When the elasticity equals zero, demand is perfectlyinelastic. There is no change in quantity demanded when there is a change in price.4. Figure 1 presents a supply-and-demand diagram, showing the equilibrium price, P,the equilibrium quantity, Q, and the total revenue received by producers. Totalrevenue equals the equilibrium price times the equilibrium quantity, which is thearea of the rectangle shown in the figure.Figure 15. If demand is elastic, an increase in price reduces total revenue. With elasticdemand, the quantity demanded falls by a greater percentage than the price rises.As a result, total revenue moves in the opposite direction as the price. Thus, ifprice rises, total revenue falls.6. A good with income elasticity less than zero is called an inferior good because asincome rises, the quantity demanded declines.7. The price elasticity of supply is calculated as the percentage change in quantitysupplied divided by the percentage change in price. It measures how much quantitysupplied responds to changes in price.8. If a fixed quantity of a good is available and no more can be made, the priceelasticity of supply is zero. Regardless of the percentage change in price, therewill be no change in the quantity supplied.9. Destruction of half of the fava bean crop is more likely to hurt fava bean farmersif the demand for fava beans is very elastic. Destruction of half of the cropcauses the supply curve to shift to the left resulting in a higher price of favabeans. When demand is very elastic, an increase in price leads to a decrease intotal revenue because the decrease in quantity demanded outweighs the increase inprice.Quick Check Multiple Choice1. a2. b3. d4. c5. a6. cProblems and Applications1. a. Mystery novels have more elastic demand than required textbooks because mysterynovels have close substitutes and are a luxury good, while required textbooksare a necessity with no close substitutes. If the price of mystery novels wereto rise, readers could substitute other types of novels, or buy fewer novelsaltogether. But if the price of required textbooks were to rise, students wouldhave little choice but to pay the higher price. Thus, the quantity demanded ofrequired textbooks is less responsive to price than the quantity demanded ofmystery novels.b. Beethoven recordings have more elastic demand than classical music recordingsin general. Beethoven recordings are a narrower market than classical musicrecordings, so it is easier to find close substitutes for them. If the price ofBeethoven recordings were to rise, people could substitute other classicalrecordings, like Mozart. But if the price of all classical recordings were torise, substitution would be more difficult. (A transition from classical musicto rap is unlikely!) Thus, the quantity demanded of classical recordings isless responsive to price than the quantity demanded of Beethoven recordings.c. Subway rides during the next five years have more elastic demand than subwayrides during the next six months. Goods have a more elastic demand over longertime horizons. If the fare for a subway ride was to rise temporarily, consumerscould not switch to other forms of transportation without great expense orgreat inconvenience. But if the fare for a subway ride was to remain high for a long time, people would gradually switch to alternative forms of transportation. As a result, the quantity demanded of subway rides during the next six months will be less responsive to changes in the price than the quantity demanded of subway rides during the next five years.d. Root beer has more elastic demand than water. Root beer is a luxury with closesubstitutes, while water is a necessity with no close substitutes. If the price of water were to rise, consumers have little choice but to pay the higher price. But if the price of root beer were to rise, consumers could easily switch toother sodas or beverages. So the quantity demanded of root beer is moreresponsive to changes in price than the quantity demanded of water.2. a. For business travelers, the price elasticity of demand when the price oftickets rises from $200 to $250 is [(2,000 – 1,900)/1,950]/[(250 – 200)/225] = = . For vacationers, the price elasticity of demand when the price oftickets rises from $200 to $250 is [(800 – 600)/700] / [(250 – 200)/225] = = .b. The price elasticity of demand for vacationers is higher than the elasticityfor business travelers because vacationers can choose a substitute more easily than business travelers. For example, vacationers can choose a different mode of transportation (like driving or taking the train), a different destination, a different departure date, and a different return date. They may also choose to not travel at all. Business travelers are less likely to do so because their schedules are less adaptable.3. a. The percentage change in price is equal to – / x 100 = 20%. If the priceelasticity of demand is , quantity demanded will fall by 4% in the short run [ ]. If the price elasticity of demand is , quantity demanded will fall by 14% in the long run [ ].b. Over time, consumers can make adjustments to their homes by purchasingalternative heat sources such as natural gas or electric furnaces. Thus, they can respond more easily to the change in the price of heating oil in the long run than in the short run.4. If quantity demanded fell, price must have increased according to the law ofdemand. For a price increase to increase total revenue, the percentage increase in the price must be greater than the percentage decline in quantity demanded. Therefore, demand is inelastic.5. , a. The effect on the market for coffee beans is shown in Figure 2. When ahurricane destroys half of the crop, the supply of coffee beans decreases, the price of coffee beans increases, and the quantity decreases.Price DemandS 1 S 2b. The effect on the market for cups of coffee is shown in Figure 2. When theprice of coffee beans, an important input into the production of a cup ofcoffee, increases, the supply of cups of coffee decreases, the price of a cup of coffee increases, and the quantity decreases.Because cups of coffee have an inelastic demand, when the price of a cup ofcoffee increases, the total expenditure on coffee increases.c. The effect on the market for donuts is shown in Figure 3. When the price ofcoffee increases and the quantity demanded of coffee decreases, consumersdemand fewer donuts because coffee and donuts are complements. When demanddecreases, the price of donuts decreases.Because donuts have an inelastic demand, when the price of donuts decreases,the total expenditure on donuts decreases.6. a. If your income is $10,000, your price elasticity of demand as the price of DVDsrises from $8 to $10 is [(40 – 32)/36]/[(10 – 8)/9] = = 1. If your income is $12,000, the elasticity is [(50 – 45)/]/[(10 – 8)/9] = = .b. If the price is $12, your income elasticity of demand as your income increasesfrom $10,000 to $12,000 is [(30 – 24)/27]/[(12,000 – 10,000)/11,000] = = . If the price is $16, your income elasticity of demand as your income increases from $10,000 to $12,000 is [(12 – 8)/10]/[(12,000 – 10,000)/11,000] = = .7. a. If Maria always spends one-third of her income on clothing, then her incomeelasticity of clothing demand is one, because maintaining her clothingPriceFigure 3expenditures as a constant fraction of her income means the percentage changein her quantity of clothing must equal her percentage change in income.b. Maria's price elasticity of clothing demand is also one, because everypercentage point increase in the price of clothing would lead her to reduce her quantity purchased by the same percentage.c. Because Maria spends a smaller proportion of her income on clothing, then forany given price, her quantity demanded will be lower. Thus, her demand curvehas shifted to the left. Because she will again spend a constant fraction ofher income on clothing, her income and price elasticities of demand remain one.8. a. The percentage change in price (using the midpoint formula) is – / × 100%= %. Therefore, the price elasticity of demand is = , which is very elastic.b. Because the demand is inelastic, the Transit Authority's revenue rises when thefare rises.c. The elasticity estimate might be unreliable because it is only the first monthafter the fare increase. As time goes by, people may switch to other means oftransportation in response to the price increase. So the elasticity may belarger in the long run than it is in the short run.9. Walt's price elasticity of demand is zero, because he wants the same quantityregardless of the price. Jessie's price elasticity of demand is one, because he spends the same amount on gas, no matter what the price, which means hispercentage change in quantity is equal to the percentage change in price.10. a. With a price elasticity of demand of , reducing the quantity demanded ofcigarettes by 20% requires a 50% increase in price, because 20/50 = . With the price of cigarettes currently $2, this would require an increase in the priceto $ a pack using the midpoint method (note that ($ – $2)/$ = .50).b. The policy will have a larger effect five years from now than it does one yearfrom now. The elasticity is larger in the long run, because it may take sometime for people to reduce their cigarette usage. The habit of smoking is hardto break in the short run.c. Because teenagers do not have as much income as adults, they are likely to havea higher price elasticity of demand. Also, adults are more likely to beaddicted to cigarettes, making it more difficult to reduce their quantitydemanded in response to a higher price.11. To determine whether you should increase or decrease the price of admissions, youneed to know if the demand is elastic or inelastic. If demand is elastic, adecline in the price of admissions will increase total revenue. If demand isinelastic, an increase in the price of admissions will cause total revenue to rise.。
曼昆《经济学原理》Chapter 05
7
The Elasticity of Demand
• Variety of demand curves
– Demand is perfectly inelastic
• Price elasticity of demand = 0 • Demand curve is vertical
– Demand is perfectly elastic
• Midpoint method
– Two points: (Q1, P1) and (Q2, P2)
Η Ο ∆ ς Ω Λ Φ Ρ Γ Ι Η Π ∆ Θ Γ (Q2 − Q1 )/[(Q2 + Q1 )/ 2 ] = (P2 − P )/[(P2 + P )/ 2 ] 1 1
6
© 2012 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part, except for use as permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Elasticity and Its Application
PowerPoint Slides prepared by: Andreea CHIRITESCU Eastern Illinois University
© 2012 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part, except for use as permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
《经济学原理·曼昆·第三版》第5章
我们已经在一般意义上讨论了需求价格弹性，现 在我们更精确地讨论它的计量。经济学家用需求 量变动的百分比除以价格变动的百分比来计算需 求价格弹性。这就是：需求价格弹性=需求量变 动的百分比/价格变动的百分比
Percentage Change in Quantity Demanded Price Elasticity of Demand = Percentage Change in Price
需求的价格弹性是33/50，或者0.66。与此相比，从B点到A 点，价格下降了33%，而数量增加了50%，表明需求的价 格弹性是50/33，或1.5。
5.1.3 用中点法计算需求价格弹性
避免这个问题的一种方法是用中点法计算弹性；中点法不 是用标准的方法（变动量除以原先的水平）计算变动的百 分比，而是用变动量除以原先水平与最后水平的中点来计 算变动的百分比。例如，4美元和6美元的中点是5美元；因 此，根据中点法，从4美元到6美元是上升了40％;同样，从 6美元变动到4美元也是下降了40%。 因为无论变动的方向如何，中点法给出了同一个答案，所 以，在计算两点之间的需求价格弹性时通常用这种方法。
相关说明
由于一种物品的需求量与其价格负相关，所以，数量变动的百分比与 价格变动百分比总是相反的符号。在本书中我们遵循一般做法，去掉 负号，把所有价格弹性作为正数。
（1）如果价格变动1个百分点，引起需求量变动超过1个百分点 （5%），则该物品就是富有需求价格弹性（Price-elastic demand）。 （2）如果价格变动1个百分点，引起需求量变动不足1个百分点 （0.2%），则该物品就缺乏需求价格弹性（Price-inelastic demand）。 （3）一种重要的特殊情况是某物品拥有单位需求价格弹性 (Unitelastic demand)，需求量变动的百分比恰好等于价格变动的百分比。 这种特殊性表现在后面将涉及到的总收益。单位需求弹性，无论价格 怎么变化，总收益不变。
《经济学原理》第五章弹性及其应用
第五章弹性及其应用在本章中你将——了解需求弹性的含义考察决定需求弹性的因素是什么了解供给弹性的含义考察决定供给弹性的因素是什么在三个非常不同的市场上运用弹性的概念设想你是堪萨斯州一个种小麦的农民。
由于你所有的收入都来自出售小麦，所以，你尽了最大的努力来提高你的土地的产量。
你注意天气和土壤状况，检查田地预防病虫害并学习农业技术的最新进展。
你知道，你的小麦种得越多，收成之后也就卖得越多，而你的收入和生活水平也就更高。
有一天，堪萨斯州立大学宣布了一项重大发现。
该大学农学系的研究人员培育出一种小麦新杂交品种，该品种可以使农民每英亩的产量增加20%。
你对这条新闻有什么反响呢?你应该采用这种新杂交品种吗？这种发现会使你比以前状况变好呢，还是变坏？在本章中，我们将看到，这些问题的答案出人意外。
这种出人意外之处来自运用经济学最根本的工具——供给与需求——来分析小麦市场。
上一章中介绍了供给与需求。
在任何一个竞争市场上，例如小麦市场，向右上方倾斜的供给曲线代表卖者的行为，而向右下方倾斜的需求曲线代表买者的行为。
一种物品价格的调整使该物品的需求量与供给量实现平衡。
为了运用这种根本分析来解释农业科学家发现的影响，我们必须首先提出另一种工具：弹性的概念。
弹性是衡量买者与卖者对市场条件变动反响大小的指标，它使我们可以更精确地分析供给与需求。
需求弹性我们在第四章讨论需求的决定因素时，我们注意到，当一种物品的价格低时，当买者收入高时，当该物品替代品的价格高，或该物品互补品的价格低时，买者对该物品的需通常更多。
我们对需求的讨论是定性的，而不是定量的。
这就是说，我们讨论需求量变动的方向，而不是变动的大小。
为了衡量需求对其决定因素变动的反响程度，经济学家用了弹性的概念。
弹性：需求量或供给量对其决定因素中某一种的反响程度的衡量。
需求价格弹性及其决定因素需求规律说明，一种物品的价格下降使需求量增加。
需求价格弹性衡量需求量对价格变动的反响程度，是一种物品需求量对其价格变动反响程度的衡量，用需求量变动的百分比除以价格变动的百分比来计算。
- 1、下载文档前请自行甄别文档内容的完整性，平台不提供额外的编辑、内容补充、找答案等附加服务。
- 2、"仅部分预览"的文档,不可在线预览部分如存在完整性等问题,可反馈申请退款(可完整预览的文档不适用该条件!)。
- 3、如文档侵犯您的权益，请联系客服反馈,我们会尽快为您处理(人工客服工作时间：9:00-18:30)。
Computing the Price Elasticity of Demand
(100 - 50)
Price
ED
(100 50)/2 (4.00 5.00)/2
(4.00 - 5.00)
$5
4 Demand
67 percent -3 - 22 percent
Demand is price elastic
Example: If the price of an ice cream cone increases from $2.00 to $2.20 and the amount you buy falls from 10 to 8 cones the your elasticity of demand, using the midpoint formula, would be calculated as:
0 50 100 Quantity
Ranges of Elasticity
Perfectly Inelastic Quantity demanded does not respond to price changes. Perfectly Elastic Quantity demanded changes infinitely with any change in price. Unit Elastic Quantity demanded changes by the same percentage as the price.
demand with greater precision.
Price Elasticity of Demand
Price elasticity of demand is the
percentage change in quantity demanded given a percent change in the price.
A Variety of Demand Curves
Because the price elasticity of demand measures how much quantity demanded responds to the price, it is closely related to the slope of the demand curve.
Necessities versus Luxuries
Availability of Close Substitutes
Definition of the Market
Time Horizon
Determinants of Price Elasticity of Demand
Demand tends to be more elastic :
Quantity demanded does not respond strongly to price changes. Price elasticity of demand is less than one.
Elastic Demand
Quantity demanded responds strongly to changes in price. Price elasticity of demand is greater than one.
Quantity
Elasticity and Total Revenue
Total revenue is the amount paid by
buyers and received by sellers of a good. Computed as the price of the good times the quantity sold.
The price elasticity of demand is computed as the percentage change in the quantity demanded divided by the percentage change in price.
Percentage Change in Quantity Demanded Price Elasticity of Demand = Percentage Change in Price
Price
1. At any price above $4, quantity demanded is zero. $4 2. At exactly $4, consumers will buy any quantity. Demand
3. At a price below $4, quantity demanded is infinite.
Perfectly Inelastic Demand
- Elasticity equals 0
Price Demand
$5 1. An increase in price... 4
Quantity 100 2. ...leaves the quantity demanded unchanged.
Inelastic Demand
Elasticity and Its Application
Chapter 5
Elasticity . . .
… is a measure of how much buyers
and sellers respond to changes in market conditions
… allows us to analyze supply and
$3 Revenue = $240 $1 Revenue = $100
Demand
100
Demand
0 80
0
Quantity
Quantity
Elasticity and Total Revenue
With an elastic demand curve, an increase in the price leads to a decrease in quantity demanded that is proportionately larger. Thus, total revenue decreases.
Elasticity and Total Revenue: Elastic Demand
Price
An increase in price from $4 to $5...
Price
…leads to a decrease in total revenue from$200 to $100
$5 $4
Price
1. A 22% $5 increase in price... 4 Demand
Quantity 50 100 2. ...leads to a 67% decrease in quantity.
Perfectly Elastic Demand
- Elasticity equals infinity
- Elasticity equals 1
Price
1. A 22% $5 increase in price... 4 Demand
Quantity 80 100 2. ...leads to a 22% decrease in quantity.
Elastic Demand
- Elasticity is greater than 1
- Elasticity is less than 1
Price
1. A 22% $5 increase in price... 4 Demand
Quantity 90 100 2. ...leads to a 11% decrease in quantity.
Unit Elastic Demand
Revenue = $200
Demand
Demand
Revenue = $100
0
50
Quantity
0
20
Quantity
Computing the Elasticity of a Linear Demand Curve
Total Revenue (Price x Percent Change Quantity) in Price $0 200% 12 67 20 40 24 29 24 22 20 18 12 15 0 Percent Change in Quantity 15% 18 22 29 40 67 200
Computing the Price Elasticity of Demand
Price elasticity of demand Percentagechange in quatity demanded Percentagechange in price
Example: If the price of an ice cream cone increases from $2.00 to $2.20 and the amount you buy falls from 10 to 8 cones then your elasticity of demand would be calculated as:
Elasticity and Total Revenue: Inelastic Demand
Price Price
An increase in price from $1 to $3...
…leads to an increase in total revenue from$100 to $240
(10 8 ) 100 20 percent 10 2 ( 2.20 2.00) 100 10 percent 2.00
Computing the Price Elasticity of Demand Using the Midpoint Formula