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1995 AIME Problems

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1995 AIME (Answer Key)
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Instructions

  1. This is a 15-question, 3-hour examination. All answers are integers ranging from 000 to 999, inclusive. Your score will be the number of correct answers; i.e., there is neither partial credit nor a penalty for wrong answers.
  2. No aids other than scratch paper, graph paper, ruler, compass, and protractor are permitted. In particular, calculators are not permitted.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Contents

Problem 1

Square S_{1} is 1\times 1. For i\ge 1, the lengths of the sides of square S_{i+1} are half the lengths of the sides of square S_{i}, two adjacent sides of square S_{i} are perpendicular bisectors of two adjacent sides of square S_{i+1}, and the other two sides of square S_{i+1}, are the perpendicular bisectors of two adjacent sides of square S_{i+2}. The total area enclosed by at least one of S_{1}, S_{2}, S_{3}, S_{4}, S_{5} can be written in the form m/n, where m and n are relatively prime positive integers. Find m-n.

Image:AIME 1995 Problem 1.png

Solution

Problem 2

Find the last three digits of the product of the positive roots of \sqrt{1995}x^{\log_{1995}x}=x^2.

Solution

Problem 3

Starting at (0,0), an object moves in the coordinate plane via a sequence of steps, each of length one. Each step is left, right, up, or down, all four equally likely. Let p be the probability that the object reaches (2,2) in six or fewer steps. Given that p can be written in the form m/n, where m and n are relatively prime positive integers, find m+n.

Solution

Problem 4

Circles of radius 3 and 6 are externally tangent to each other and are internally tangent to a circle of radius 9. The circle of radius 9 has a chord that is a common external tangent of the other two circles. Find the square of the length of this chord.

Solution

Problem 5

For certain real values of a, b, c, and d_{}, the equation x^4+ax^3+bx^2+cx+d=0 has four non-real roots. The product of two of these roots is 13+i and the sum of the other two roots is 3+4i, where i=\sqrt{-1}. Find b.

Solution

Problem 6

Let n=2^{31}3^{19}. How many positive integer divisors of n^2 are less than n_{} but do not divide n_{}?

Solution

Problem 7

Given that (1+\sin t)(1+\cos t)=5/4 and

(1-\sin t)(1-\cos t)=\frac mn-\sqrt{k},

where k, m, and n_{} are positive integers with m_{} and n_{} relatively prime, find k+m+n.

Solution

Problem 8

For how many ordered pairs of positive integers (x,y), with y<x\le 100, are both \frac xy and \frac{x+1}{y+1} integers?

Solution

Problem 9

Triangle ABC is isosceles, with AB=AC and altitude AM=11. Suppose that there is a point D on \overline{AM} with AD=10 and \angle BDC=3\angle BAC. Then the perimeter of \triangle ABC may be written in the form a+\sqrt{b}, where a and b are integers. Find a+b.

Image:AIME_1995_Problem_9.png

Solution

Problem 10

What is the largest positive integer that is not the sum of a positive integral multiple of 42 and a positive composite integer?

Solution

Problem 11

A right rectangular prism P_{} (i.e., a rectangular parallelpiped) has sides of integral length a, b, c, with a\le b\le c. A plane parallel to one of the faces of P_{} cuts P_{} into two prisms, one of which is similar to P_{}, and both of which have nonzero volume. Given that b=1995, for how many ordered triples (a, b, c) does such a plane exist?

Solution

Problem 12

Pyramid OABCD has square base ABCD, congruent edges \overline{OA}, \overline{OB}, \overline{OC}, and \overline{OD}, and \angle AOB=45^\circ. Let \theta be the measure of the dihedral angle formed by faces OAB and OBC. Given that \cos \theta=m+\sqrt{n}, where m_{} and n_{} are integers, find m+n.

Solution

Problem 13

Let f(n) be the integer closest to \sqrt[4]{n}. Find \sum_{k=1}^{1995}\frac 1{f(k)}.

Solution

Problem 14

In a circle of radius 42, two chords of length 78 intersect at a point whose distance from the center is 18. The two chords divide the interior of the circle into four regions. Two of these regions are bordered by segments of unequal lenghts, and the area of either of them can be expressed uniquley in the form m\pi-n\sqrt{d}, where m, n, and d_{} are positive integers and d_{} is not divisible by the square of any prime number. Find m+n+d.

Solution

Problem 15

Let p_{} be the probability that, in the process of repeatedly flipping a fair coin, one will encounter a run of 5 heads before one encounters a run of 2 tails. Given that p_{} can be written in the form m/n where m_{} and n_{} are relatively prime positive integers, find m+n.

Solution

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