500
                                In the World Series, two teams, A and B, play each other until one team has won 5 games.  For example, the "word" ABBAAAA represents a 7-game series in which team A wins games 1, 4, 5, 6 and 7.  What is the number of possible different 7-game series won by team A?
                                6! / (4! 2!)  = 15