The 32nd Canadian Mathematical Olympiads
2000年第32届加拿大数学奥林匹克 
 Three runners start together and run around a track length 3L at different constant speeds, not necessarily in the same direction (so, for example, they may all run clockwise, or one may run clockwise). Show that there is a moment when any given runner is a distance L or more from both the other runners (where distance is measured around the track in the shorter direction) .
 How many permutations of 1901, 1902, 1903, ... , 2000 are such that none of the sums of the first n permuted numbers is divisible by 3 (for n = 1, 2, 3, ... , 2000) ?
 Show that in any sequence of 2000 integers each with absolute value not exceeding 1000 such that the sequence has sum 1, we can find a subsequence of one or more terms with zero sum .
 ABCD is a convex quadrilateral with AB = BC, ∠CBD = 2 ∠ADB, and ∠ABD = 2 ∠CDB . Show that AD = DC .
 A nonincreasing sequence of 100 nonnegative reals has the sum of the first two terms at most 100 and the sum of the remaining terms at most 100. What is the largest possible value for the sum of the squares of the terms ?

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