20th AIME1 2002

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1.  A licence plate is 3 letters followed by 3 digits. If all possible licence plates are equally likely, what is the probability that a plate has either a letter palindrome or a digit palindrome (or both)?
2.  20 equal circles are packed in honeycomb fashion in a rectangle. The outer rows have 7 circles, and the middle row has 6. The outer circles touch the sides of the rectangle. Find the long side of the rectangle divided by the short side.
3.  Jane is 25. Dick's age is d > 25. In n years both will have two-digit ages which are obtained by transposing digits (so if Jane will be 36, Dick will be 63). How many possible pairs (d, n) are there?
4.  The sequence x1, x2, x3, ... is defined by xk = 1/(k2 + k). A sum of consecutive terms xm + xm+1 + ... + xn = 1/29. Find m and n.
5.  D is a regular 12-gon. How many squares (in the plane of D) have two or more of their vertices as vertices of D?
6.  The solutions to log225x + log64y = 4, logx225 - logy64 = 1 are (x, y) = (x1, y1) and (x2, y2). Find log30(x1y1x2y2).
7.  What are the first three digits after the decimal point in (102002 + 1)10/7? You may use the extended binomial theorem: (x + y)r = xr(1 + 4 (y/x) + r(r-1)/2! (y/x)2 + r(r-1)(r-2)/3! (y/x)3 + ...) for r real and |x/y| < 1
8.  Find the smallest integer k for which there is more than one non-decreasing sequence of positive integers a1, a2, a3, ... such that a9 = k and an+2 = an+1 + an.
9.  A, B, C paint a long line of fence-posts. A paints the first, then every ath, B paints the second then every bth, C paints the third, then every cth. Every post gets painted just once. Find all possible triples (a, b, c).
10.  ABC is a triangle with angle B = 90o. AD is an angle bisector. E lies on the side AB with AE = 3, EB = 9, and F lies on the side AC with AF = 10, FC = 27. EF meets AD at G. Find the nearest integer to area GDCF.
11.  A cube with two faces ABCD, BCEF, has side 12. The point P is on the face BCEF a perpendicular distance 5 from the edge BC and from the edge CE. A beam of light leaves A and travels along AP, at P it is reflected inside the cube. Each time it strikes a face it is reflected. How far does it travel before it hits a vertex?
12.  The complex sequence z0, z1, z2, ... is defined by z0 = i + 1/137 and zn+1 = (zn + i)/(zn - i). Find z2002.
13.  The triangle ABC has AB = 24. The median CE is extended to meet the circumcircle at F. CE = 27, and the median AD = 18. Find area ABF.
14.  S is a set of positive integers containing 1 and 2002. No elements are larger than 2002. For every n in S, the arithmetic mean of the other elements of S is an integer. What is the largest possible number of elements of S?
15.  ABCDEFGH is a polyhedron. Face ABCD is a square side 12. Face ABFG is a trapezoid with GF parallel to AB and GF = 6, AG = BF = 8. Face CDE is an isosceles triangle with ED = EC = 14. E is a distance 12 from the plane ABCD. The other faces are EFG, ADEG and BCEF. Find EG2.

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
4 Aug 2003
Last updated/corrected 4 Aug 03