# 1985 AIME Problems

## Contents

## Problem 1

Let , and for let. Calculate the product .

## Problem 2

When a right triangle is rotated about one leg, the volume of the cone produced is . When the triangle is rotated about the other leg, the volume of the cone produced is . What is the length (in cm) of the hypotenuse of the triangle?

## Problem 3

Find if , , and are positive integers which satisfy , where .

## Problem 4

A small square is constructed inside a square of area 1 by dividing each side of the unit square into equal parts, and then connecting the vertices to the division points closest to the opposite vertices. Find the value of if the the area of the small square is exactly .

## Problem 5

A sequence of integers is chosen so that for each . What is the sum of the first 2001 terms of this sequence if the sum of the first 1492 terms is 1985, and the sum of the first 1985 terms is 1492?

## Problem 6

As shown in the figure, triangle is divided into six smaller triangles by lines drawn from the vertices through a common interior point. The areas of four of these triangles are as indicated. Find the area of triangle .

## Problem 7

Assume that , , , and are positive integers such that , , and . Determine .

## Problem 8

The sum of the following seven numbers is exactly 19: , , , , , , . It is desired to replace each by an integer approximation , , so that the sum of the 's is also 19 and so that , the maximum of the "errors" , the maximum absolute value of the difference, is as small as possible. For this minimum , what is ?

## Problem 9

In a circle, parallel chords of lengths 2, 3, and 4 determine central angles of , , and radians, respectively, where . If , which is a positive rational number, is expressed as a fraction in lowest terms, what is the sum of its numerator and denominator?

## Problem 10

How many of the first 1000 positive integers can be expressed in the form

,

where is a real number, and denotes the greatest integer less than or equal to ?

## Problem 11

An ellipse has foci at and in the -plane and is tangent to the -axis. What is the length of its major axis?

## Problem 12

Let , , and be the vertices of a regular tetrahedron each of whose edges measures 1 meter. A bug, starting from vertex , observes the following rule: at each vertex it chooses one of the three edges meeting at that vertex, each edge being equally likely to be chosen, and crawls along that edge to the vertex at its opposite end. Let be the probability that the bug is at vertex when it has crawled exactly 7 meters. Find the value of .

## Problem 13

The numbers in the sequence , , , , are of the form , where For each , let be the greatest common divisor of and . Find the maximum value of as ranges through the positive integers.

## Problem 14

In a tournament each player played exactly one game against each of the other players. In each game the winner was awarded 1 point, the loser got 0 points, and each of the two players earned 1/2 point if the game was a tie. After the completion of the tournament, it was found that exactly half of the points earned by each player were earned against the ten players with the least number of points. (In particular, each of the ten lowest scoring players earned half of her/his points against the other nine of the ten). What was the total number of players in the tournament?

## Problem 15

Three 12 cm 12 cm squares are each cut into two pieces and , as shown in the first figure below, by joining the midpoints of two adjacent sides. These six pieces are then attached to a regular hexagon, as shown in the second figure, so as to fold into a polyhedron. What is the volume (in ) of this polyhedron?