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2010AMC10 美国数学竞赛 A 卷

2010 AMC10 美国数学竞赛 A 卷 1. Mary’s top book shelf holds five books with the following widths, in centimeters: 6, 1/2, 1, 2.5, and 10. What is the average book width, in centimeters? (A) 1 (B) 2 (C) 3 (D) 4 (E) 5

2. Four identical squares and one rectangle are placed together to form one large square as shown. The length of the rectangle is how many times as large as its width? (A) 5/4 (D) 2 (B) 4/3 (E) 3 (C) 3/2

3. Tyrone had 97 marbles and Eric had 11 marbles. Tyrone then gave some of his marbles to Eric so that Tyrone ended with twice as many marbles as Eric. How many marbles did Tyrone give to Eric? (A) 3 (B) 13 (C) 18 (D) 25 (E) 29

4. A book that is to be recorded onto compact discs takes 412 minutes to read aloud. Each disc can hold up to 56 minutes of reading. Assume that the smallest possible number of discs is used and that each disc contains the same length of reading. How many minutes of reading will each disc contain? (A) 50.2 (B) 51.5 (C) 52.4 (D) 53.8 (E) 55.2

5. The area of a circle whose circumference is 24π is kπ . What is the value of k?

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2010AMC10 美国数学竞赛 A 卷

(A) 6

(B) 12

(C) 24

(D) 36

(E) 144

6. For positive numbers x and y the operation Φ (x, y) is defined as Φ( x, y) = x ? . What is Φ(2, Φ（2, 2）? ) (A)

2 (B) 1 3

1 y

(C)

4 3

(D)

5 3

(E) 2

7. Crystal has a running course marked out for her daily run. She starts this run by heading due north for one mile. She then runs northeast for one mile, then southeast for one mile. The last portion of her run takes her on a straight line back to where she started. How far, in miles, is this last portion of her run? (A) 1 (B)

2

(C)

3

(D) 2

(E) 2 2

8. Tony works 2 hours a day and is paid $0.50 per hour for each full year of his age. During a six month period Tony worked 50 days and earned $630. How old was Tony at the end of the six month period? (A) 9 (B) 11 (C) 12 (D) 13 (E) 14

9. A palindrome, such as 83438, is a number that remains the same when its digits are reversed. The numbers x and x+32 are three-digit and four-digit palindromes, respectively. What is the sum of the digits of x? (A) 20 (B) 21 (C) 22 (D) 23 (E) 24

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2010AMC10 美国数学竞赛 A 卷

10. Marvin had a birthday on Tuesday, May 27 in the leap year 2008. In what year will his birthday next fall on a Saturday? (A) 2011 (B) 2012 (C) 2013 (D) 2015 (E) 2017

11. The length of the interval of solutions of the inequality a ≤ 2 x + 3 ≤ b is 10. What is b-a? (A) 6 (B) 10 (C) 15 (D) 20 (E) 30

12. Logan is constructing a scaled model of his town. The city’s water tower stands 40 meters high, and the top portion is a sphere that holds 100,000 liters of water. Logan’s miniature water tower holds 0.1 liters. How tall, in meters, should Logan make his tower? (A) 0.04 (B)

0.4

π

(C) 0.4

(D)

4

π

(E) 4

13. Angelina drove at an average rate of 80 kph and then stopped 20 minutes for gas. After the stop, she drove at an average rate of 100 kph. Altogether she drove 250 km in a total trip time of 3 hours including the stop. Which equation could be used to solve for the time t in hours that she drove before her stop? (A) 80t + 100( ? t ) = 250 (D) 90t = 250

8 3 8 3

(B) 80t = 250

(C) 100t = 250

(E) 80( ? t ) + 100t = 250

14. Triangle ABC has AB=2AC. Let D and E be on AB and BC respectively, such that

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2010AMC10 美国数学竞赛 A 卷

∠BAE=∠ACD. Let F be the intersection of segments AE and CD, and suppose that △CFE is equilateral. What is ∠ACB? (A) 60° (B) 75° (C) 90° (D) 105° (E) 120°

15. In a magical swamp there are two species of talking amphibians; toads, whose statements are always true, and frogs, whose statements are always false. Four amphibians, Brian, Chris, LeRoy, and Mike live together in this swamp, and they make the following statements. Brian:”Mike and I are different species.” Chris:”LeRoy is a frog.” Mike:”Of the four of us, at least two are toads.” How many of these amphibians are frogs? (A) 0 (B) 1 (C) 2 (D) 3 (E) 4

16. Non degenerate △ABC has integer side lengths, BD is an angle bisector, AD=3, and DC=8. What is the smallest possible value of the perimeter? (A) 30 (B) 33 (C) 35 (D) 36 (E) 37

17. A solid cube has side length 3 inches. A 2-inch by 2-inch square hole is cut into the center of each face. The edges of each cut are parallel to the edges of the cube, and each hole goes all the way through the cube. What is the volume, in cubic inches, of the remaining solid?

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2010AMC10 美国数学竞赛 A 卷

(A) 7

(B) 8

(C) 10

(D) 12

(E) 15

18. Bernardo randomly picks 3distinct numbers from the set {1, 2, 3, 4, 5, 6, 7, 8, 9} and arranges them in descending order to form a 3-digit number. Silvia randomly picks 3 distinct numbers from the set {1, 2, 3, 4, 5, 6, 7, 8} and also arranges them in descending order to form a 3-digit number. What is the probability that Bernardo’s number is larger than Silvia’s number? (A)

47 72

(B)

37 56

(C)

2 3

(D)

49 72

(E)

39 56

19. Equiangular hexagon ABCDEF has side lengths AB=CD=EF=1 and BC=DE=FA=r. The area of △ACE is 70% of the area of the hexagon. What is the sum of all possible values of r? (A)

4 3 3

(B)

10 3

(C) 4

(D)

17 4

(E) 6

20. A fly trapped inside a cubical box with side length 1 meter decides to relieve its boredom by visiting each corner of the box. It will begin and end in the same corner and visit each of the other corners exactly once. To get from a corner to any other corner, it will either fly or crawl in a straight line. What is the maximum possible length, in meters, of its path? (A) 4 + 4 2 (D) 4 2 + 4 3 (B) 2 + 4 2 + 2 3 (E) 3 2 + 5 3 (C) 2 + 3 2 + 3 3

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2010AMC10 美国数学竞赛 A 卷

21. The polynomial x3 + ax 2 + bx ? 2010 has three positive integer zeros. What is the smallest possible value of a? (A) 78 (B) 88 (C) 98 (D) 108 (E) 118

22. Eight points are chosen on a circle, and chords are drawn connecting every pair of points. No three chords intersect in a single point inside the circle. How many triangles with all three vertices is the interior of the circle are created? (A) 28 (B) 56 (C) 70 (D) 84 (E) 140

23. Each of 2010 boxes in a line contains a single red marble, and for 1 ≤ k ≤ 2010 , the kth position also contains k white marbles. Isabella begins at the first box and successively draws a single marble at random from each box, in order. She stops when she first draws a red marble. Let P(n) be the probability that Isabella stops after drawing exactly n marbles. What is the smallest value of n for which P(n) ≤ (A) 45 (B) 63 (C) 64 (D) 201 (E) 1005

1 ? 2010

24. The number obtained from the last two nonzero digits of 90! Is equal to n. What is n? (A) 12 (B) 32 (C) 48 (D) 52 (E) 68

25. Jim starts with a positive integer n and creates a sequence of numbers. Each successive number is obtained by subtracting the largest possible integer square less

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2010AMC10 美国数学竞赛 A 卷

than or equal to the current number until zero is reached. For example, if Jim starts with n=55, then his sequence contains 5 numbers: 55 55-72= 6 6-22= 2 2-12= 1 1-12= 0 Let N be the smallest number for which Jim’s sequence has 8 numbers. What is the units digit of N? (A) 1 (B) 3 (C) 5 (D) 7 (E) 9

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