AMC真题(附答案)1
2013年美国数学竞赛AMC12A真题
Square has side length . Point is on , and the area of is . What is ?
Problem 2
A softball team played ten games, scoring , and runs. They lost by one run in
exactly five games. In each of the other games, they scored twice as many runs as their opponent.
How many total runs did their opponents score?
Problem 3
A flower bouquet contains pink roses, red roses, pink carnations, and red carnations. One third of the pink flowers are roses, three fourths of the red flowers are carnations, and six tenths of the flowers are pink. What percent of the flowers are carnations?
Problem 4
What is the value of
Tom, Dorothy, and Sammy went on a vacation and agreed to split the costs evenly. During their trip
Tom paid $, Dorothy paid $, and Sammy paid $. In order to share the costs equally, Tom
gave Sammy dollars, and Dorothy gave Sammy dollars. What is ?
Problem 6
In a recent basketball game, Shenille attempted only three-point shots and two-point shots. She was
successful on of her three-point shots and of her two-point shots. Shenille
attempted shots. How many points did she score?
Problem 7
The sequence has the property that every term beginning with the third is the sum
of the previous two. That is,Suppose that and . What
is ?
Problem 8
Given that and are distinct nonzero real numbers such that , what is ?
Problem 9
In , and . Points and are on sides , , and ,
respectively, such that and are parallel to and , respectively. What is the perimeter of parallelogram ?
Problem 10
Let be the set of positive integers for which has the repeating decimal
representation with and different digits. What is the sum of the elements of ?
Problem 11
Triangle is equilateral with . Points and are on and points and are
on such that both and are parallel to . Furthermore, triangle and
trapezoids and all have the same perimeter. What is ?
Problem 12
The angles in a particular triangle are in arithmetic progression, and the side lengths are . The
sum of the possible values of x equals where , and are positive integers. What
is ?
Let points and . Quadrilateral is cut into equal
area pieces by a line passing through . This line intersects at point , where these fractions are in lowest terms. What is ?
Problem 14
The sequence
, , , ,
is an arithmetic progression. What is ?
Problem 15
Rabbits Peter and Pauline have three offspring—Flopsie, Mopsie, and Cotton-tail. These five rabbits are to be distributed to four different pet stores so that no store gets both a parent and a child. It is not required that every store gets a rabbit. In how many different ways can this be done?
Problem 16
, , are three piles of rocks. The mean weight of the rocks in is pounds, the mean weight of
the rocks in is pounds, the mean weight of the rocks in the combined piles and is pounds, and the mean weight of the rocks in the combined piles and is pounds. What is the greatest possible integer value for the mean in pounds of the rocks in the combined piles and ?
Problem 17
A group of pirates agree to divide a treasure chest of gold coins among themselves as follows.
The pirate to take a share takes of the coins that remain in the chest. The number of coins
initially in the chest is the smallest number for which this arrangement will allow each pirate to receive
a positive whole number of coins. How many coins does the pirate receive?
Problem 18
Six spheres of radius are positioned so that their centers are at the vertices of a regular hexagon of side length . The six spheres are internally tangent to a larger sphere whose center is the center of the hexagon. An eighth sphere is externally tangent to the six smaller spheres and internally tangent to
the larger sphere. What is the radius of this eighth sphere?
Problem 19
In , , and . A circle with center and radius intersects at
points and . Moreover and have integer lengths. What is ?
Problem 20
Let be the set . For , define to mean that
either or . How many ordered triples of elements of have the
property that , , and ?
Problem 21
Consider . Which of the following intervals contains ?
A palindrome is a nonnegative integer number that reads the same forwards and backwards when written in base 10 with no leading zeros. A 6-digit palindrome is chosen uniformly at random. What is the probability that is also a palindrome?
Problem 23
is a square of side length . Point is on such that . The square region
bounded by is rotated counterclockwise with center , sweeping out a region whose area
is , where , , and are positive integers and . What is ?
Problem 24
Three distinct segments are chosen at random among the segments whose end-points are the vertices of a regular 12-gon. What is the probability that the lengths of these three segments are the three side lengths of a triangle with positive area?
Problem 25
Let be defined by . How many complex numbers are there such
that and both the real and the imaginary parts of are integers with absolute value at
most ?
Answer Key
1. E
2. C
3. E
4. C
5. B
6. B
7. C
8. D
9. C
10.D
11.C
12.A
13.B
14.B
15.D
16.E
17.D
18.B
19.D
20.B
21.A
22.E
23.C
24.E
25.A