MathDB
Math Prize 2010 Problem 19

Source:

November 14, 2010
geometrysymmetryprobabilityexpected value

Problem Statement

Let SS be the set of 81 points (x,y)(x, y) such that xx and yy are integers from āˆ’4-4 through 44. Let AA, BB, and CC be random points chosen independently from SS, with each of the 81 points being equally likely. (The points AA, BB, and CC do not have to be different.) Let KK be the area of the (possibly degenerate) triangle ABCABC. What is the expected value (average value) of K2K^2 ?