## 2012 AIME I真题

#### 答案解析请参考文末

## Problem 1

Find the number of positive integers with three not necessarily distinct digits, , with and such that both and are multiples of .

## Problem 2

The terms of an arithmetic sequence add to . The first term of the sequence is increased by , the second term is increased by , the third term is increased by , and in general, the th term is increased by the th odd positive integer. The terms of the new sequence add to . Find the sum of the first, last, and middle term of the original sequence.

## Problem 3

Nine people sit down for dinner where there are three choices of meals. Three people order the beef meal, three order the chicken meal, and three order the fish meal. The waiter serves the nine meals in random order. Find the number of ways in which the waiter could serve the meal types to the nine people so that exactly one person receives the type of meal ordered by that person.

## Problem 4

Butch and Sundance need to get out of Dodge. To travel as quickly as possible, each alternates walking and riding their only horse, Sparky, as follows. Butch begins by walking while Sundance rides. When Sundance reaches the first of the hitching posts that are conveniently located at one-mile intervals along their route, he ties Sparky to the post and begins walking. When Butch reaches Sparky, he rides until he passes Sundance, then leaves Sparky at the next hitching post and resumes walking, and they continue in this manner. Sparky, Butch, and Sundance walk at and miles per hour, respectively. The first time Butch and Sundance meet at a milepost, they are miles from Dodge, and they have been traveling for minutes. Find .

## Problem 5

Let be the set of all binary integers that can be written using exactly zeros and ones where leading zeros are allowed. If all possible subtractions are performed in which one element of is subtracted from another, find the number of times the answer is obtained.

## Problem 6

The complex numbers and satisfy and the imaginary part of is , for relatively prime positive integers and with Find

## Problem 7

At each of the sixteen circles in the network below stands a student. A total of coins are distributed among the sixteen students. All at once, all students give away all their coins by passing an equal number of coins to each of their neighbors in the network. After the trade, all students have the same number of coins as they started with. Find the number of coins the student standing at the center circle had originally.

## Problem 8

Cube labeled as shown below, has edge length and is cut by a plane passing through vertex and the midpoints and of and respectively. The plane divides the cube into two solids. The volume of the larger of the two solids can be written in the form where and are relatively prime positive integers. Find

## Problem 9

Let and be positive real numbers that satisfyThe value of can be expressed in the form where and are relatively prime positive integers. Find

## Problem 10

Let be the set of all perfect squares whose rightmost three digits in base are . Let be the set of all numbers of the form , where is in . In other words, is the set of numbers that result when the last three digits of each number in are truncated. Find the remainder when the tenth smallest element of is divided by .

## Problem 11

A frog begins at and makes a sequence of jumps according to the following rule: from the frog jumps to which may be any of the points or There are points with that can be reached by a sequence of such jumps. Find the remainder when is divided by

## Problem 12

Let be a right triangle with right angle at Let and be points on with between and such that and trisect If then can be written as where and are relatively prime positive integers, and is a positive integer not divisible by the square of any prime. Find

## Problem 13

Three concentric circles have radii and An equilateral triangle with one vertex on each circle has side length The largest possible area of the triangle can be written as where and are positive integers, and are relatively prime, and is not divisible by the square of any prime. Find

## Problem 14

Complex numbers and are zeros of a polynomial and The points corresponding to and in the complex plane are the vertices of a right triangle with hypotenuse Find

## Problem 15

There are mathematicians seated around a circular table with seats numbered in clockwise order. After a break they again sit around the table. The mathematicians note that there is a positive integer such that

() for each the mathematician who was seated in seat before the break is seated in seat after the break (where seat is seat );

() for every pair of mathematicians, the number of mathematicians sitting between them after the break, counting in both the clockwise and the counterclockwise directions, is different from either of the number of mathematicians sitting between them before the break.

Find the number of possible values of with

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