MathDB
Coordinate Probability

Source:

December 6, 2005
analytic geometryprobabilitynumber theoryrelatively prime

Problem Statement

Let SS be the set of points whose coordinates x,x, y,y, and zz are integers that satisfy 0x2,0\le x\le2, 0y3,0\le y\le3, and 0z4.0\le z\le4. Two distinct points are randomly chosen from S.S. The probability that the midpoint of the segment they determine also belongs to SS is m/n,m/n, where mm and nn are relatively prime positive integers. Find m+n.m+n.