国际经济学(克鲁格曼)教材答案

Chapter 3

1．Home has 1200 units of labor available. It can produce two goods, apples and bananas. The unit labor requirement in apple production is 3, while in banana production it is 2. a ．Graph out the production possibilities frontier:

b ．What is the opportunity cost of apples in terms of bananas?

5.1=Lb

La a a c ．In the absence of trade, what would the price of apples in terms of bananas be?

In the absence of trade, since labor is the only factor of production and supply decisions are

determined by the attempts of individuals to maximize their earnings in a competitive economy, only when Lb La b a /a a /P P =will both goods be produced. So 1.5 /P P b a =

2．Home is as described in problem 1. There is now also another country, Foreign, with a

labor force of 800. Foreign ’s unit labor requirement in apple production is 5, while in banana production it is 1.

a ．Graph Foreign ’s production possibilities frontier:

b ．Construct the world relative supply curve.

Home's PPF 0200400600800

200400600800Q apple Q banana Foreign's PPF

02004006008001000

80160240320400Q*apple Q*banana

3．Now suppose world relative demand takes the following form: Demand for apples/demand

for bananas = price of bananas/price of apples.

a ．Graph the relative demand curve along with the relative supply curve:

a b b a /P P /D D =

∵When the market achieves its equilibrium, we have 1b a )(D D -**=++=b

a b b a a P P Q Q Q Q ∴RD is a hyperbola x

y 1=

b ．What is the equilibrium relative price of apples?

The equilibrium relative price of apples is determined by the intersection of the RD and RS

curves.

RD: y

x 1= RS: 5]5,5.1[5.1],5.0(5

.0)5.0,0[=∈=⎪⎩

⎪⎨⎧+∞∈=∈y y y x x x ∴25

.0==y x

∴2/=b P a P e e

c ．Describe the pattern of trade.

∵b a b e a e b a P P P P P P ///>>**

∴In this two-country world, Home will specialize in the apple production, export apples and import bananas. Foreign will specialize in the banana production, export bananas and import apples.

d ．Show that both Hom

e and Foreign gain from trade.

International trade allows Home and Foreign to consume anywhere within the colored

lines, which lie outside the countries ’ production possibility frontiers. And the indirect method, specializing in producing only one production then trade with other country, is a more efficient method than direct production. In the absence of trade, Home could gain three bananas by foregoing two apples, and Foreign could gain by one foregoing five bananas. Trade allows each country to trade two bananas for one apple. Home could then gain four bananas by foregoing two apples while Foreign could gain one apple by foregoing only two bananas. So both Home and Foreign gain from trade.

4．Suppose that instead of 1200 workers, Home had 2400. Find the equilibrium relative price. What can you say about the efficiency of world production and the division of the gains from trade between Home and Foreign in this case?

RD: y

x 1= RS: 5]5,5.1[5.1],1(1

)1,0[=∈=⎪⎩

⎪⎨⎧+∞∈=∈y y y x x x ∴5.132==

y x ∴5.1/=b P a P e e