15th AIME 1997

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1.  How many of 1, 2, 3, ... , 1000 can be written as the difference of the squares of two non-negative integers?
2.  The 9 horizontal and 9 vertical lines on an 8 x 8 chessboard form r rectangles including s squares. Find s/r in lowest terms.
3.  M is a 2-digit number ab, and N is a 3-digit number cde. We have 9·M·N = abcde. Find M, N.
4.  Circles radii 5, 5, 8, k are mutually externally tangent. Find k.
5.  The closest approximation to r = 0.abcd (where any of a, b, c, d may be zero) of the form 1/n or 2/n is 2/7. How many possible values are there for r?
6.  A1A2...An is a regular polygon. An equilateral triangle A1BA2 is constructed outside the polygon. What is the largest n for which BA1An can be consecutive vertices of a regular polygon?
7.  A car travels at 2/3 mile/min due east. A circular storm starts with its center 110 miles due north of the car and travels southeast at 1/√2 miles/min. The car enters the storm circle at time t1 mins and leaves it at t2. Find (t1 + t2)/2.
8.  How many 4 x 4 arrays of 1s and -1s are there with all rows and all columns having zero sum?
9.  The real number x has 2 < x2 < 3 and the fractional parts of 1/x and x2 are the same. Find x12 - 144/x.
10.  A card can be red, blue or green, have light, medium or dark shade, and show a circle, square or triangle. There are 27 cards, one for each possible combination. How many possible 3-card subsets are there such that for each of the three characteristics (color, shade, shape) the cards in the subset are all the same or all different?
11.  Find [100(cos 1o + cos 2o + ... + cos 44o)/(sin 1o + sin 2o + ... + sin 44o)].
12.  a, b, c, d are non-zero reals and f(x) = (ax + b)/(cx + d). We have f(19) = 19, f(97) = 97 and f(f(x)) = x for all x (except -d/c). Find the unique y not in the range of f.
13.  Let S = {(x, y) : | ||x| - 2| - 1| + | ||y| - 2| - 1| = 1. If S is made out of wire, what is the total length of wire is required?
14.  v, w are roots of z1997 = 1 chosen at random. Find the probability that |v + w| >= √(2 + √3).
15.  Find the area of the largest equilateral triangle that can be inscribed in a rectangle with sides 10 and 11.

Answers

To avoid possible copyright problems, I have changed the wording, but not the substance, of the problems.

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© John Scholes
jscholes@kalva.demon.co.uk
1 Aug 2003
Last updated/corrected 1 Aug 03