MathDB
Card Probability

Source:

December 8, 2005
probabilitynumber theoryrelatively prime

Problem Statement

A deck of forty cards consists of four 1's, four 2's,..., and four 10's. A matching pair (two cards with the same number) is removed from the deck. Given that these cards are not returned to the deck, let m/nm/n be the probability that two randomly selected cards also form a pair, where mm and nn are relatively prime positive integers. Find m+n.m+n.