21st AIME2 2003

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1.  The product N of three positive integers is 6 times their sum. One of the integers is the sum of the other two. Find the sum of all possible values of N.
2.  N is the largest multiple of 8 which has no two digits the same. What is N mod 1000?
3.  How many 7-letter sequences are there which use only A, B, C (and not necessarily all of those), with A never immediately followed by B, B never immediately followed by C, and C never immediately followed by A?
4.  T is a regular tetrahedron. T' is the tetrahedron whose vertices are the midpoints of the faces of T. Find vol T'/vol T.
5.  A log is in the shape of a right circular cylinder diameter 12. Two plane cuts are made, the first perpendicular to the axis of the log and the second at a 45o angle to the first, so that the line of intersection of the two planes touches the log at a single point. The two cuts remove a wedge from the log. Find its volume.
6.  A triangle has sides 13, 14, 15. It is rotated through 180o about its centroid to form an overlapping triangle. Find the area of the union of the two triangles.
7.  ABCD is a rhombus. The circumradii of ABD, ACD are 12.5, 25. Find the area of the rhombus.
8.  Corresponding terms of two arithmetic progressions are multiplied to give the sequence 1440, 1716, 1848, ... . Find the eighth term.
9.  The roots of x4 - x3 - x2 - 1 = 0 are a, b, c, d. Find p(a) + p(b) + p(c) + p(d), where p(x) = x6 - x5 - x3 - x2 - x.
10.  Find the largest possible integer n such that √n + √(n+60) = √m for some non-square integer m.
11.  ABC has AC = 7, BC = 24, angle C = 90o. M is the midpoint of AB, D lies on the same side of AB as C and had DA = DB = 15. Find area CDM.
12.  n people vote for one of 27 candidates. Each candidate's percentage of the vote is at least 1 less than his number of votes. What is the smallest possible value of n? (So if a candidate gets m votes, then 100m/n ≤ m-1.)
13.  A bug moves around a wire triangle. At each vertex it has 1/2 chance of moving towards each of the other two vertices. What is the probability that after crawling along 10 edges it reaches its starting point?
14.  ABCDEF is a convex hexagon with all sides equal and opposite sides parallel. Angle FAB = 120o. The y-coordinates of A, B are 0, 2 respectively, and the y-coordinates of the other vertices are 4, 6, 8, 10 in some order. Find its area.
15.  The distinct roots of the polynomial x47 + 2x46 + 3x45 + ... + 24x24 + 23x23 + 22x22 + ... + 2x2 + x are z1, z2, ... , zn. Let zk2 have imaginary part bki. Find |b1| + |b2| + ... + |bn|.

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 15 Mar 04