# 1988 AIME Problems

## Contents

## Problem 1

One commercially available ten-button lock may be opened by depressing -- in any order -- the correct five buttons. The sample shown below has as its combination. Suppose that these locks are redesigned so that sets of as many as nine buttons or as few as one button could serve as combinations. How many additional combinations would this allow?

## Problem 2

For any positive integer , let denote the square of the sum of the digits of . For , let . Find .

## Problem 3

Find if .

## Problem 4

Suppose that for . Suppose further that

What is the smallest possible value of ?

## Problem 5

Let , in lowest terms, be the probability that a randomly chosen positive divisor of is an integer multiple of . Find .

## Problem 6

It is possible to place positive integers into the vacant twenty-one squares of the 5 times 5 square shown below so that the numbers in each row and column form arithmetic sequences. Find the number that must occupy the vacant square marked by the asterisk (*).

## Problem 7

In triangle , , and the altitude from divides into segments of length and . What is the area of triangle ?

## Problem 8

The function , defined on the set of ordered pairs of positive integers, satisfies the following properties:

Calculate .

## Problem 9

Find the smallest positive integer whose cube ends in `888`.

## Problem 10

A convex polyhedron has for its faces 12 squares, 8 regular hexagons, and 6 regular octagons. At each vertex of the polyhedron one square, one hexagon, and one octagon meet. How many segments joining vertices of the polyhedron lie in the interior of the polyhedron rather than along an edge or a face?

## Problem 11

Let be complex numbers. A line in the complex plane is called a mean line for the points if contains points (complex numbers) such that

For the numbers , , , , and , there is a unique mean line with y-intercept . Find the slope of this mean line.

## Problem 12

Let be an interior point of triangle and extend lines from the vertices through to the opposite sides. Let , , , and denote the lengths of the segments indicated in the figure. Find the product if and .

## Problem 13

Find if and are integers such that is a factor of .

## Problem 14

Let be the graph of , and denote by the reflection of in the line . Let the equation of be written in the form Find the product .

## Problem 15

In an office at various times during the day, the boss gives the secretary a letter to type, each time putting the letter on top of the pile in the secretary's in-box. When there is time, the secretary takes the top letter off the pile and types it. There are nine letters to be typed during the day, and the boss delivers them in the order 1, 2, 3, 4, 5, 6, 7, 8, 9.

While leaving for lunch, the secretary tells a colleague that letter 8 has already been typed, but says nothing else about the morning's typing. The colleague wonders which of the nine letters remain to be typed after lunch and in what order they will be typed. Based upon the above information, how many such after-lunch typing orders are possible? (That there are no letters left to be typed is one of the possibilities.)