美国数学学会中学生数学竞赛真题和答案解析2015AMC8 Solutions
美国数学学会中学生数学竞赛真题和答案解析2012AMC8-solutions
American Mathematics Competitions
28th Annual
AMC 8
American Mathematics Contest 8 Tuesday, November 13, 2012
This Solutions Pamphlet gives at least one solution for each problem on this year’s exam and shows that all the problems can be solved using material normally associated with the mathematics curriculum for students in eighth grade or below. These solutions are by no means the only ones possible, nor are they necessarily superior to others the reader may devise. We hope that teachers will share these solutions with their students. However, the publication, reproduction, or communication of the problems or solutions of the AMC 8 during the period when students are eligible to participate seriously jeopardizes the integrity of the results. Dissemination at any time via copier, telephone, email, internet or media of any type is a violation of the competition rules.
amc8题集
AMC8是美国数学竞赛的一个初级级别，适合8年级及以下的学生参加。
以下是AMC8的部分题目：
卡西的商店正在制作一个高尔夫球奖品。
他必须给一颗高尔夫球面上的300个小凹洞着色，如果每着色一个小凹洞需要2秒钟，试问共需多分钟才能完成？
Alicia, Brenda, and Clby were the candidates in a recent election. The votes were counted and the results were: Alicia: 45%, Brenda: 35%, Clby: 20%. 5% of Brenda’s votes were invalid. Which candidate has the largest percentage of valid votes?
Which of the following values is largest?
对于想要提升数学水平、准备参加AMC8竞赛的学生，建议做相关的题目来提高解题技巧和思维能力。
同时，也可以参考一些数学竞赛的教材和辅导书，如《数学竞赛大全》、《初中数学竞赛教程》等。
2015 年美国大学生数学建模竞赛 MCM
2015 年美国大学生数学建模竞赛MCM、ICM 试题2015 MCM A: Eradicating EbolaThe world medical association has announced that their new medication could stop Ebola and cure patients whose disease is not advanced. Build a realistic, sensible, and useful model that considers not only the spread of the disease, the quantity of the medicine needed, possible feasible delivery systems, locations of delivery, speed of manufacturing of the vaccine or drug, but also any other critical factors your team considers necessary as part of the model to optimize the eradication of Ebola, or at least its current strain. In addition to your modeling approach for the contest, prepare a 1-2 page non-technical letter for the world medical association to use in their announcement.2015 MCM B: Searching for a lost planeRecall the lost Malaysian flight MH370. Build a generic mathematical model that could assist “searchers” in planning a useful search for a lost plane feared to have crashed in open water such as the Atlantic, Pacific, Indian, Southern, or Arctic Ocean while flying from Point A to Point B. Assume that there are no signals from the downed plane. Your model should recognize that there are many different types of planes for which we might be searching and that there are many different types of search planes, often using different electronics or sensors. Additionally, prepare a 1-2 page non-technical paper for the airlines to use in their press conferences concerning their plan for future searches.。
2015年AMC8试题及答案
Copyright © 2016 Art of Problem Solving How many square yards of carpet are required to cover a rectangular floor that is feet long and feetwide? (There are 3 feet in a yard.)First, we multiply to get that you need square feet of carpet you need to cover. Since thereare square feet in a square yard, you divide by to get square yards, so our answer is .Since there are feet in a yard, we divide by to get , andby to get . To find the area of the carpet, we then multiply these two values together to get .2015 AMC 8 (Problems • Answer Key • Resources(/Forum/resources.php?c=182&cid=42&year=2015))Preceded byFirst Problem Followed by Problem 21 •2 •3 •4 •5 •6 •7 •8 •9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 •19 • 20 • 21• 22 • 23 • 24 • 25All AJHSME/AMC 8 Problems and SolutionsThe problems on this page are copyrighted by the Mathematical Association of America ()'s American Mathematics Competitions ().Placement:Easy GeometryRetrieved from "/wiki/index.php?title=2015_AMC_8_Problems/Problem_1&oldid=80323"SolutionSolution 2See AlsoPoint is the center of the regular octagon , and is the midpoint of the side What fraction of the area of the octagon is shaded?Since octagon is a regular octagon, it is split into equal parts, such as triangles, etc. These parts, since they are all equal, are of the octagon each. The shaded region consists of of these equal parts plus half of another, so the fraction of the octagon that is shaded isThe octagon has been divided up into identical triangles (and thus they each have equal area). Since the shaded region occupiesout of the total triangles, the answer is .For starters what I find helpful is to divide the whole octagon up into triangles as shown here:Now it is just a matter of counting the larger triangles remember that and are notfull triangles and are only half for these purposes. We count it up and we get a total ofof the shape shaded. We then simplify it to get our answer of .2015 AMC 8 (Problems • Answer Key • Resources(/Forum/resources.php?c=182&cid=42&year=2015))Preceded byProblem 1Followed by Problem 31 •2 •3 •4 •5 •6 •7 •8 •9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 •19 • 20 • 21 • 22 • 23 • 24 • 25All AJHSME/AMC 8 Problems and SolutionsSolution 3See AlsoCopyright © 2016 Art of Problem Solving Jack and Jill are going swimming at a pool that is one mile from their house. They leave home simultaneously. Jill rides her bicycle to the pool at a constant speed of miles per hour. Jack walks tothe pool at a constant speed of miles per hour. How many minutes before Jack does Jill arrive?Using , we can set up an equation for when Jill arrives at the swimming pool:Solving for , we get that Jill gets to the pool inof an hour, which is minutes. Doing the same for Jack, we get that Jack arrives at the pool inof an hour, which in turn is minutes. Thus, Jill has to waitminutes for Jack to arrive at the pool.2015 AMC 8 (Problems • Answer Key • Resources(/Forum/resources.php?c=182&cid=42&year=2015))Preceded byProblem 2Followed by Problem 41 •2 •3 •4 •5 •6 •7 •8 •9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 •19 • 20 • 21 • 22 • 23 • 24 • 25All AJHSME/AMC 8 Problems and Solutions The problems on this page are copyrighted by the Mathematical Association of America ()'s American Mathematics Competitions ().Retrieved from "/wiki/index.php?title=2015_AMC_8_Problems/Problem_3&oldid=81064"SolutionSee AlsoCopyright © 2016 Art of Problem SolvingThe Centerville Middle School chess team consists of two boys and three girls. A photographer wants to take a picture of the team to appear in the local newspaper. She decides to have them sit in a row with a boy ateach end and the three girls in the middle. How many such arrangements are possible?There are ways to order the boys on the end, and there are ways to order the girls in the middle.We get the answer to be .2015 AMC 8 (Problems • Answer Key • Resources(/Forum/resources.php?c=182&cid=42&year=2015))Preceded byProblem 3Followed by Problem 51 •2 •3 •4 •5 •6 •7 •8 •9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 •19 • 20 • 21 • 22 • 23 • 24 • 25All AJHSME/AMC 8 Problems and Solutions The problems on this page are copyrighted by the Mathematical Association of America ()'s American Mathematics Competitions ().Retrieved from "/wiki/index.php?title=2015_AMC_8_Problems/Problem_4&oldid=73224"SolutionSee AlsoCopyright © 2016 Art of Problem SolvingBilly's basketball team scored the following points over the course of the first 11 games of the season:If his team scores 40 in the 12th game, which of the following statistics will show an increase?When they score a on the next game, the range increases from to . This means the increased.Because is less than the score of every game they've played so far, the measures of center will neverrise. Only measures of spread, such as the, may increase.2015 AMC 8 (Problems • Answer Key • Resources(/Forum/resources.php?c=182&cid=42&year=2015))Preceded byProblem 4Followed by Problem 61 •2 •3 •4 •5 •6 •7 •8 •9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 •19 • 20 • 21 • 22• 23 • 24 • 25All AJHSME/AMC 8 Problems and SolutionsThe problems on this page are copyrighted by the Mathematical Association of America ()'s American Mathematics Competitions ().Retrieved from "/wiki/index.php?title=2015_AMC_8_Problems/Problem_5&oldid=80825"SolutionSolution 2Copyright © 2016 Art of Problem Solving In , , and . What is the area of?We know the semi-perimeter of is . Next, we use Heron's Formula to find that the area of the triangle is just .Splitting the isosceles triangle in half, we get a right triangle with hypotenuseand leg . Using the Pythagorean Theorem , we know the height is. Now that we know the height, the area is.2015 AMC 8 (Problems • Answer Key • Resources(/Forum/resources.php?c=182&cid=42&year=2015))Preceded byProblem 5Followed by Problem 71 •2 •3 •4 •5 •6 •7 •8 •9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 •19 • 20 • 21 • 22 • 23 •24 • 25All AJHSME/AMC 8 Problems and SolutionsThe problems on this page are copyrighted by the Mathematical Association of America ()'s American Mathematics Competitions ().Retrieved from "/wiki/index.php?title=2015_AMC_8_Problems/Problem_6&oldid=80483"Solution 1Solution 2See AlsoEach of two boxes contains three chips numbered , , . A chip is drawn randomly from each box and thenumbers on the two chips are multiplied. What is the probability that their product is even?We can instead find the probability that their product is odd, and subtract this from . In order to get an odd product, we have to draw an odd number from each box. We have a probability of drawing an odd numberfrom one box, so there is a probability of having an odd product. Thus, there is a probability of having an even product.You can also make this problem into a spinner problem. You have the first spinner with equally divided sections, andYou make a second spinner that is identical to the first, with equal sections of ,, and . If the first spinner lands on , to be even, it must land on two. You write down the first combination of numbers . Next, if the spinner lands on , it can land on any number on the second spinner. We now have the combinations of . Finally, if the first spinner ends on , we have Since there arepossible combinations, and we have evens, the final answer is.2015 AMC 8 (Problems • Answer Key • Resources(/Forum/resources.php?c=182&cid=42&year=2015))Preceded byProblem 6Followed by Problem 81 •2 •3 •4 •5 •6 •7 •8 •9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 •19 • 20 • 21 • 22 • 23 • 24 • 25All AJHSME/AMC 8 Problems and SolutionsThe problems on this page are copyrighted by the Mathematical Association of America ()'s American Mathematics Competitions ().Retrieved from "/wiki/index.php?title=2015_AMC_8_Problems/Problem_7&oldid=73737"SolutionSolution 2See AlsoCopyright © 2016 Art of Problem Solving What is the smallest whole number larger than the perimeter of any triangle with a side of length and aside of length ?We know from the triangle inequality that the last side, , fulfills . Adding to both sides of the inequality, we get , and becauseis the perimeter ofour triangle, is our answer.2015 AMC 8 (Problems • Answer Key • Resources(/Forum/resources.php?c=182&cid=42&year=2015))Preceded byProblem 7Followed by Problem 91 •2 •3 •4 •5 •6 •7 •8 •9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 •19 • 20 • 21 • 22 • 23• 24 • 25All AJHSME/AMC 8 Problems and SolutionsThe problems on this page are copyrighted by the Mathematical Association of America ()'s American Mathematics Competitions ().Retrieved from "/wiki/index.php?title=2015_AMC_8_Problems/Problem_8&oldid=78101"SolutionSee AlsoCopyright © 2016 Art of Problem Solving On her first day of work, Janabel sold one widget. On day two, she sold three widgets. On day three, she sold five widgets, and on each succeeding day, she sold two more widgets than she had sold on the previousday. How many widgets in total had Janabel sold after working days?The sum of is The sum is just the sum of the first odd integers, which is2015 AMC 8 (Problems • Answer Key • Resources(/Forum/resources.php?c=182&cid=42&year=2015))Preceded byProblem 8Followed by Problem 101 •2 •3 •4 •5 •6 •7 •8 •9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 •19 • 20 • 21 • 22 • 23 • 24 • 25All AJHSME/AMC 8 Problems and Solutions The problems on this page are copyrighted by the Mathematical Association of America ()'sAmerican Mathematics Competitions ().Retrieved from "/wiki/index.php?title=2015_AMC_8_Problems/Problem_9&oldid=79933"Solution 1Solution 2See AlsoCopyright © 2016 Art of Problem SolvingHow many integers betweenandhave four distinct digits?The question can be rephrased to "How many four-digit positive integers have four distinct digits?",since numbers between and are four-digit integers. There are choices for the first number, since it cannot be , there are only choices left for the second number since it must differ from the first, choices for the third number, since it must differ from the first two, and choices for the fourth number,since it must differ from all three. This means there are integersbetweenandwith four distinct digits.2015 AMC 8 (Problems • Answer Key • Resources(/Forum/resources.php?c=182&cid=42&year=2015))Preceded by Problem 9Followed by Problem 111 •2 •3 •4 •5 •6 •7 •8 •9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 •19 • 20 • 21 • 22• 23 • 24 • 25All AJHSME/AMC 8 Problems and SolutionsThe problems on this page are copyrighted by the Mathematical Association of America ()'sAmerican Mathematics Competitions ().Retrieved from "/wiki/index.php?title=2015_AMC_8_Problems/Problem_10&oldid=81128"Solution 1See AlsoCopyright © 2016 Art of Problem SolvingIn the small country of Mathland, all automobile license plates have four symbols. The first must be a vowel (A, E, I, O, or U), the second and third must be two different letters among the 21 non-vowels, and thefourth must be a digit (0 through 9). If the symbols are chosen at random subject to these conditions, whatis the probability that the plate will read "AMC8"?There is one favorable case, which is the license plate says "AMC8". We must now find how many total cases there are. There are choices for the first letter (since it must be a vowel), choices for the second letter (since it must be of consonants), choices for the third letter (since it must differ from the second letter), and choices for the number. This leads to total possible license plates. That means the probability of a license plate saying "AMC8" is.The probability of choosing A as the first letter is . The probability of choosing next is. Theprobability of choosing C as the third letter is(since there areother consonants to choose fromother then M). The probability of having as the last number is . We multiply all these to obtain2015 AMC 8 (Problems • Answer Key • Resources(/Forum/resources.php?c=182&cid=42&year=2015))Preceded by Problem 10Followed by Problem 121 •2 •3 •4 •5 •6 •7 •8 •9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 •19 • 20 • 21 • 22 • 23 •24 • 25All AJHSME/AMC 8 Problems and SolutionsThe problems on this page are copyrighted by the Mathematical Association of America ()'sAmerican Mathematics Competitions ().Retrieved from "/wiki/index.php?title=2015_AMC_8_Problems/Problem_11&oldid=73554"Solution 1Solution 2See AlsoHow many pairs of parallel edges, such asandorand, does a cube have?We first count the number of pairs of parallel lines that are in the same direction as. The pairs ofparallel lines are ,, , , ,and . These are pairs total. We can do the same for the lines in the same direction asand. This means there aretotal pairs of parallel lines.Pick a random edge. Given another edge, the probability that it is parallel to this edge is. Keep in mind we already used one edge. There are edges so pairs. So our answer is.2015 AMC 8 (Problems • Answer Key • Resources(/Forum/resources.php?c=182&cid=42&year=2015))Preceded by Problem 11Followed by Problem 131 •2 •3 •4 •5 •6 •7 •8 •9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 •19 • 20 • 21 • 22 • 23 • 24 • 25All AJHSME/AMC 8 Problems and SolutionsSolution 1Solution 2See AlsoCopyright © 2016 Art of Problem SolvingHow many subsets of two elements can be removed from the set so thatthe mean (average) of the remaining numbers is 6?Since there will be elements after removal, and their mean is , we know their sum is . We also knowthat the sum of the set pre-removal is . Thus, the sum of the elements removed is .There are onlysubsets of elements that sum to:.2015 AMC 8 (Problems • Answer Key • Resources(/Forum/resources.php?c=182&cid=42&year=2015))Preceded by Problem 12Followed by Problem 141 •2 •3 •4 •5 •6 •7 •8 •9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 •19 • 20 • 21 • 22• 23 • 24 • 25All AJHSME/AMC 8 Problems and SolutionsThe problems on this page are copyrighted by the Mathematical Association of America ()'sAmerican Mathematics Competitions ().Retrieved from "/wiki/index.php?title=2015_AMC_8_Problems/Problem_13&oldid=73377"SolutionSee AlsoLet our numbers be , where is odd. Then our sum is . The only answer choice that cannot be written as , where is odd, is .If the four consecutive odd integers are and then the sum is . All the integers are divisible by except .If the four consecutive odd integers are and , the sum is , and divided by gives . This means that must be even. The only integer that does notgive an even integer when divided by is , so the answer is .From Solution 1, we have the sum of the numbers to be equal to . Taking mod 8 gives usfor some residue and for some odd integer . Since , we can express it as the equation for some integer . Multiplying 4 to each side of the equation yields , and taking mod 8 gets us , so . All the answer choicesexcept choice D is a multiple of 8, and since 100 satisfies all the conditions the answer is .The problems on this page are copyrighted by the Mathematical Association of America ()'s American Mathematics Competitions ().Copyright © 2016 Art of Problem SolvingAt Euler Middle School,students voted on two issues in a school referendum with the following results:voted in favor of the first issue and voted in favor of the second issue. If there were exactlystudents who voted against both issues, how many students voted in favor of both issues?We can see that this is a Venn Diagram Problem.First, we analyze the information given. There are students. Let's use A as the first issue and B asthe second issue.students were for the A, and students were for B. There were also students against both A andB.Solving this without a Venn Diagram, we subtract away from the total,. Out of the remaining,we havepeople for A andpeople for B. We add this up to get. Since that is more than what we need, we subtract fromto getThere are 198 people. We know that 29 people voted against both the first issue and the second issue. That leaves us with 169 people that voted for at least one of them. If 119 people voted for both of them, then that would leave 20 people out of the vote, because 149 is less than 198 people. 198-149 is 20, so to make it even, we have to take 20 away from the 119 people, which leaves us with2015 AMC 8 (Problems • Answer Key • Resources(/Forum/resources.php?c=182&cid=42&year=2015))Preceded by Problem 14Followed by Problem 161 •2 •3 •4 •5 •6 •7 •8 •9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 •19 • 20 • 21 • 22• 23 • 24 • 25All AJHSME/AMC 8 Problems and SolutionsThe problems on this page are copyrighted by the Mathematical Association of America ()'sAmerican Mathematics Competitions ().Retrieved from "/wiki/index.php?title=2015_AMC_8_Problems/Problem_15&oldid=80999"Solution 1Solution 2See AlsoCopyright © 2016 Art of Problem SolvingIn a middle-school mentoring program, a number of the sixth graders are paired with a ninth-grade student as a buddy. No ninth grader is assigned more than one sixth-grade buddy. If of all the ninth graders are paired withof all the sixth graders, what fraction of the total number of sixth and ninth graders have a buddy?Let the number of sixth graders be , and the number of ninth graders be . Thus, , whichsimplifies to. Since we are trying to find the value of, we can just substitute forinto the equation. We then get a value ofWe see that the minimum number of ninth graders is , because if there arethen there is ninth grader with a buddy, which would mean sixth graders with a buddy, and that's impossible. With ninth graders, of them are in the buddy program, so theresixth graders total, two of whom have a buddy. Thus,the desired fraction is .2015 AMC 8 (Problems • Answer Key • Resources(/Forum/resources.php?c=182&cid=42&year=2015))Preceded by Problem 15Followed by Problem 171 •2 •3 •4 •5 •6 •7 •8 •9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 •19 • 20 • 21 • 22• 23 • 24 • 25All AJHSME/AMC 8 Problems and SolutionsThe problems on this page are copyrighted by the Mathematical Association of America ()'sAmerican Mathematics Competitions ().Retrieved from "/wiki/index.php?title=2015_AMC_8_Problems/Problem_16&oldid=73512"Solution 1Solution 2See AlsoSo and .This gives , which gives , which then givesSolution 2, is obviously constantso , plug into the first one and it's miles to schoolWe set up an equation in terms of the distance and the speed In miles per hour. We have SoAn arithmetic sequence is a sequence in which each term after the first is obtained by adding a constant to the previous term. For example, is an arithmetic sequence with five terms, in which thefirst term is and the constant added is . Each row and each column in this array is an arithmetic sequence with five terms. What is the value of ?We begin filling in the table. The top row has a first term and a fifth term , so we have the common difference is . This means we can fill in the first row of the table:The fifth row has a first term of and a fifth term of , so the common difference is. We can fill in the fifth row of the table as shown:Copyright © 2016 Art of Problem SolvingWe must find the third term of the arithmetic sequence with a first term of and a fifth term of . The common difference of this sequence is, so the third term is.The middle term of the first row is, since the middle number is just the average in anarithmetic sequence. Similarly, the middle of the bottom row is . Applying this again forthe middle column, the answer is.The value ofis simply the average of the average values of both diagonals that contain. This is2015 AMC 8 (Problems • Answer Key • Resources(/Forum/resources.php?c=182&cid=42&year=2015))Preceded by Problem 17Followed by Problem 191 •2 •3 •4 •5 •6 •7 •8 •9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 •19 • 20 • 21 • 22 • 23 • 24• 25All AJHSME/AMC 8 Problems and SolutionsThe problems on this page are copyrighted by the Mathematical Association of America ()'sAmerican Mathematics Competitions ().Retrieved from "/wiki/index.php?title=2015_AMC_8_Problems/Problem_18&oldid=73460"Solution 2Solution 3See AlsoA triangle with vertices as , , and is plotted on a grid. What fraction of the grid is covered by the triangle?The area of is equal to half the product of its base and height. By the Pythagorean Theorem, we find its height is , and its base is . We multiply these and divideby to find the of the triangle is . Since the grid has an area of , the fraction of the grid covered by the triangle is .Note angle is right, thus the area is thus the fraction of the total isCopyright © 2016 Art of Problem SolvingBy the Shoelace theorem, the area of.This means the fraction of the total area isThe smallest rectangle that follows the grid lines and completely encloses has an area of,where splits the rectangle into four triangles. The area ofis therefore . That means thattakes upof the grid.Using Pick's Theorem, the area of the triangle is. Therefore, the triangle takes upof the grid.2015 AMC 8 (Problems • Answer Key • Resources(/Forum/resources.php?c=182&cid=42&year=2015))Preceded by Problem 18Followed by Problem 201 •2 •3 •4 •5 •6 •7 •8 •9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 •19 • 20 • 21 • 22• 23 • 24 • 25All AJHSME/AMC 8 Problems and SolutionsThe problems on this page are copyrighted by the Mathematical Association of America ()'sAmerican Mathematics Competitions ().Retrieved from "/wiki/index.php?title=2015_AMC_8_Problems/Problem_19&oldid=75879"Solution 4Solution 5See AlsoRalph went to the store and bought 12 pairs of socks for a total of $24. Some of the socks he bought cost $1a pair, some of the socks he bought cost $3 a pair, and some of the socks he bought cost $4 a pair. If hebought at least one pair of each type, how many pairs of $1 socks did Ralph buy?So let there be pairs of socks, pairs ofsocks, pairs of socks.We have,, and.Now we subtract to find , and . It follows that is a multiple of and is amultiple of , so since , we must have .Therefore, , and it follows that. Now, asdesired.Since the total cost of the socks was and Ralph boughtpairs, the average cost of each pair ofsocks is.There are two ways to make packages of socks that average to . You can have:Twopairs and one pair (package adds up to )Onepair and onepair (package adds up to)So now we need to solvewhere is the number of packages and is the number of packages. We see our only solution (thathas at least one of each pair of sock) is , which yields the answer of.2015 AMC 8 (Problems • Answer Key • Resources(/Forum/resources.php?c=182&cid=42&year=2015))Preceded by Problem 19Followed by Problem 211 •2 •3 •4 •5 •6 •7 •8 •9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 •19• 20 • 21 • 22 • 23 • 24 • 25All AJHSME/AMC 8 Problems and SolutionsThe problems on this page are copyrighted by the Mathematical Association of America ()'sAmerican Mathematics Competitions ().Retrieved from "/wiki/index.php?2015 AMC 8 Problems/Problem 20Solution 1Solution 2See AlsoIn the given figure hexagon is equiangular, andare squares with areasandrespectively, is equilateral and . What is the area of ?.Clearly, since is a side of a square with area , . Now, since , we have .Now, is a side of a square with area, so . Since is equilateral, . Lastly, is a right triangle. We see that, so is a right triangle with legs and . Now, its area is .2015 AMC 8 (Problems • Answer Key • Resources(/Forum/resources.php?c=182&cid=42&year=2015))Preceded byProblem 20Followed byProblem 221 •2 •3 •4 •5 •6 •7 •8 •9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 •21•22 • 23 • 24 • 25All AJHSME/AMC 8 Problems and SolutionsThe problems on this page are copyrighted by the Mathematical Association of America ()'s American Mathematics Competitions ().Retrieved from "/wiki/index.php?title=2015_AMC_8_Problems/Problem_21&oldid=73361"2015 AMC 8 Problems/Problem 21SolutionSee AlsoCopyright © 2016 Art of Problem SolvingCopyright © 2016 Art of Problem SolvingOn June 1, a group of students is standing in rows, with 15 students in each row. On June 2, the same group is standing with all of the students in one long row. On June 3, the same group is standing with just one student in each row. On June 4, the same group is standing with 6 students in each row. This processcontinues through June 12 with a different number of students per row each day. However, on June 13, they cannot find a new way of organizing the students. What is the smallest possible number of students in thegroup?As we read through this text, we find that the given information means that the number of students in thegroup has factors, since each arrangement is a factor. The smallest integer with factors is.2015 AMC 8 (Problems • Answer Key • Resources(/Forum/resources.php?c=182&cid=42&year=2015))Preceded by Problem 21Followed by Problem 231 •2 •3 •4 •5 •6 •7 •8 •9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 •19 • 20 • 21 • 22 • 23 • 24 •25All AJHSME/AMC 8 Problems and SolutionsThe problems on this page are copyrighted by the Mathematical Association of America ()'sAmerican Mathematics Competitions ().Retrieved from "/wiki/index.php?title=2015_AMC_8_Problems/Problem_22&oldid=73359"SolutionSee Also。
美国数学竞赛AMC8 -- 2008年真题解析(英文解析+中文解析)
美国数学竞赛AMC8 – 2008年真题解析(英文解析+中文解析)Problem 1Answer: BSolution:50-12-24=14中文解析：总共花的钱是：12+12*2=36元。
剩余50-36=14元。
答案是BProblem 2Answer: ASolution:We can derive that c=8,L=6, U=7,and E=1. Therefore, the answer is 8671.中文解析：这10个字母的对应关系是： B -0；E-1; S-2; ......K -9. 按照这个对应关系：C-8，L-6，U-7，E-1. 即8671. 答案是A。
Problem 3Answer: ASolution:We can go backwards by days, but we can also backwards by weeks. If we go backwards by weeks, we see that February 6 is a Friday. If we now go backwards by days, February 1 is a Sunday.中文解析：13日是周五，则13-7=6，即6日也是周五，则倒推2月1日是周日。
答案是A。
Problem 4Answer: CSolution:The area outside the small triangle but inside the large triangle is 16-1=15. This is equally distributed between the three trapezoids. Each trapezoid has an area of 15/3=5.中文解析：大三角形的面积等于小的等边三角形的面积加上3个梯形的面积。
据此，三个梯形的面积是16-1=15. 每个梯形的面积是15/3=5. 答案是C。
AMC8(美国数学竞赛)历年真题、答案及中英文解析
AMC8（美国数学竞赛）历年真题、答案及中英文解析艾蕾特教育的AMC8 美国数学竞赛考试历年真题、答案及中英文解析：AMC8-2020年：真题 --- 答案---解析（英文解析+中文解析）AMC8 - 2019年：真题----答案----解析（英文解析+中文解析）AMC8 - 2018年：真题----答案----解析（英文解析+中文解析）AMC8 - 2017年：真题----答案----解析（英文解析+中文解析）AMC8 - 2016年：真题----答案----解析（英文解析+中文解析）AMC8 - 2015年：真题----答案----解析（英文解析+中文解析）AMC8 - 2014年：真题----答案----解析（英文解析+中文解析）AMC8 - 2013年：真题----答案----解析（英文解析+中文解析）AMC8 - 2012年：真题----答案----解析（英文解析+中文解析）析）AMC8 - 2010年：真题----答案----解析（英文解析+中文解析）AMC8 - 2009年：真题----答案----解析（英文解析+中文解析）AMC8 - 2008年：真题----答案----解析（英文解析+中文解析）AMC8 - 2007年：真题----答案----解析（英文解析+中文解析）AMC8 - 2006年：真题----答案----解析（英文解析+中文解析）AMC8 - 2005年：真题----答案----解析（英文解析+中文解析）AMC8 - 2004年：真题----答案----解析（英文解析+中文解析）AMC8 - 2003年：真题----答案----解析（英文解析+中文解析）AMC8 - 2002年：真题----答案----解析（英文解析+中文解析）AMC8 - 2001年：真题----答案----解析（英文解析+中文解析）AMC8 - 2000年：真题----答案----解析（英文解析+中文解析）析）AMC8 - 1998年：真题----答案----解析（英文解析+中文解析）AMC8 - 1997年：真题----答案----解析（英文解析+中文解析）AMC8 - 1996年：真题----答案----解析（英文解析+中文解析）AMC8 - 1995年：真题----答案----解析（英文解析+中文解析）AMC8 - 1994年：真题----答案----解析（英文解析+中文解析）AMC8 - 1993年：真题----答案----解析（英文解析+中文解析）AMC8 - 1992年：真题----答案----解析（英文解析+中文解析）AMC8 - 1991年：真题----答案----解析（英文解析+中文解析）AMC8 - 1990年：真题----答案----解析（英文解析+中文解析）AMC8 - 1989年：真题----答案----解析（英文解析+中文解析）AMC8 - 1988年：真题----答案----解析（英文解析+中文解析）析）AMC8 - 1986年：真题----答案----解析（英文解析+中文解析）AMC8 - 1985年：真题----答案----解析（英文解析+中文解析）◆AMC介绍◆AMC（American Mathematics Competitions) 由美国数学协会（MAA）组织的数学竞赛，分为 AMC8 、 AMC10、 AMC12 。
美国数学竞赛AMC8 -- 2008年真题解析(英文解析+中文解析)
美国数学竞赛AMC8 – 2008年真题解析(英文解析+中文解析)Problem 1Answer: BSolution:50-12-24=14中文解析：总共花的钱是：12+12*2=36元。
剩余50-36=14元。
答案是BProblem 2Answer: ASolution:We can derive that c=8,L=6, U=7,and E=1. Therefore, the answer is 8671.中文解析：这10个字母的对应关系是： B -0；E-1; S-2; ......K -9. 按照这个对应关系：C-8，L-6，U-7，E-1. 即8671. 答案是A。
Problem 3Answer: ASolution:We can go backwards by days, but we can also backwards by weeks. If we go backwards by weeks, we see that February 6 is a Friday. If we now go backwards by days, February 1 is a Sunday.中文解析：13日是周五，则13-7=6，即6日也是周五，则倒推2月1日是周日。
答案是A。
Problem 4Answer: CSolution:The area outside the small triangle but inside the large triangle is 16-1=15. This is equally distributed between the three trapezoids. Each trapezoid has an area of 15/3=5.中文解析：大三角形的面积等于小的等边三角形的面积加上3个梯形的面积。
据此，三个梯形的面积是16-1=15. 每个梯形的面积是15/3=5. 答案是C。
美国数学竞赛AMC8 -- 2006年真题解析(英文解析+中文解析)
美国数学竞赛AMC8 – 2006年真题解析(英文解析+中文解析) \Problem 1Answer: DSolution:The three prices round to $2, $5, and $10, which has a sum of 17.中文解析：三件商品价格先近似取整，然后求和：2+5+10=17. 答案是D。
Problem 2Answer: CSolution:As the AMC 8 only rewards 1 point for each correct answer, everything is irrelevant except the number Billy answered correctly，13.中文解析：正确的题目每题1分，错误或没做的题目都是0分，做对13题的得分应该是13. 答案是C。
Problem 3Answer: ASolution:When Elisa started, she finished a lap in 25/10=2.5 minutes. Now, she finishes a lap is 24/12=2 minutes. The difference is 2.5-2=0.5中文解析：开始25分钟游10圈，平均2.5分钟游1圈。
后来24分钟游12圈，平均2分钟游1圈。
速度从2.5分钟提高到2分钟，提高了0.5分钟，即1/2 分钟。
答案是A。
Problem 4Answer: BSolution:If the spinner goes clockwise 2+1/4 revolutions and then counterclockwise 3+3/4 revolutions, it ultimately goes counterclockwise 1+1/2 which brings the spinner pointing east.中文解析：最初方向指向西，转整数圈不改变指针方向。
美国数学竞赛往年试题及答案
美国数学竞赛往年试题及答案试题一：一个圆的半径为 \( r \) 厘米，求圆的周长。
答案：圆的周长 \( C \) 可以用公式 \( C = 2\pi r \) 计算，其中\( \pi \) 是圆周率，大约等于3.14。
试题二：如果一个直角三角形的两条直角边分别为3厘米和4厘米，求斜边的长度。
答案：根据勾股定理，斜边 \( c \) 的长度可以通过公式 \( c =\sqrt{a^2 + b^2} \) 计算，其中 \( a \) 和 \( b \) 是直角边的长度。
所以斜边的长度为 \( c = \sqrt{3^2 + 4^2} = \sqrt{9 + 16} = \sqrt{25} = 5 \) 厘米。
试题三：一个数列的前三项是1, 1, 2。
从第四项开始，每一项都是前三项的和。
求第10项的值。
答案：数列的前几项为：1, 1, 2, 4, 7, 13, 24, 44, 81, 149。
第10项的值为149。
试题四：在一个不透明的袋子里，有3个红球和2个蓝球。
随机抽取2个球，求至少抽到1个红球的概率。
答案：总共有 \( \binom{5}{2} = 10 \) 种抽取2个球的组合。
至少抽到1个红球的组合有 \( \binom{3}{1} \times \binom{2}{1} +\binom{3}{2} = 6 + 3 = 9 \) 种。
所以概率为 \( \frac{9}{10} \)。
试题五：一个函数 \( f(x) = x^2 - 6x + 8 \)，求其顶点坐标。
答案：顶点的 \( x \) 坐标可以通过公式 \( x = -\frac{b}{2a} \) 计算，其中 \( a = 1 \) 和 \( b = -6 \)。
所以 \( x = -\frac{-6}{2\times 1} = 3 \)。
将 \( x = 3 \) 代入函数得到 \( y = 3^2 - 6\times 3 + 8 = -1 \)。
美国数学竞赛AMC8 -- 2005年真题解析(英文解析+中文解析)
美国数学竞赛AMC8 – 2005年真题解析(英文解析+中文解析)Problem 1Answer: BSolution:If x is the number, then 2x=60 and x=30. Dividing the number by 2 yields 15.中文解析：按照Connie的计算，这个数乘以2是60，可知这个数是30. 应该做的计算是30除以2，因而正确答案应该是15. 答案是B。
Problem 2Answer: CSolution:Karl paid 5*2.5=$12.5. 20% of this cost that he saved is 12.5*0.2=$2.5.中文解析：Karl按原价买了5个文件夹，支付的费用是：2.5*5=12.5. 折扣价是：1.25*0.8=10。
如果Karl 等一天，可以省2.5元。
答案是C.Problem 3Answer: DSolution:Rotating square ABCD counterclockwise 45° so that the line of symmetry BD is a vertical line makes it easier to see that 4 squares need to be colored to match its corresponding square.中文解析：如上图所示，以BD为对称轴，标蓝色的方块需要涂黑。
共4块，答案是D。
Problem 4Answer: CSolution:The perimeter of the triangle is 6.1+8.2+9.7=24cm. A square's perimeter is four times its side length, since all its side lengths are equal. If the square's perimeter is 24, the side length is24/4=6, and the area is 6*6=36.中文解析：三角形的周长是：6.1+8.2+9.7=24. 正方形的周长和三角形相等，也是24，则其边长是24/4=6. 其面积是：6*6=36. 答案是C。
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This Solutions Pamphlet gives at least one solution for each problem on this year’s exam and shows that all the problems can be solved using material normally associated with the mathematics curriculum for students in eighth grade or below. These solutions are by no means the only ones possible, nor are they necessarily superior to others the reader may devise.
We hope that teachers will share these solutions with their students. However, the publication, reproduction, or communication of the problems or solutions of the AMC 8 during the period when students are eligible to participate seriously jeopardizes the integrity of the results. Dissemination at any time via copier, telephone, email, internet or media of any type is a violation of the competition rules.
Correspondence about the problems and solutions should be addressed to:
Prof. Norbert Kuenzi, AMC 8 Chair
934 Nicolet Ave
Oshkosh, WI 54901-1634
Orders for prior year exam questions and solutions pamphlets should be addressed to:
MAA American Mathematics Competitions
Attn: Publications
PO Box 471
Annapolis Junction, MD 20701
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