500
In the World Series, two teams, A and B, play each other until one team has won 4 games. For example the "word" ABBAAA represents a 6-game series in which team A wins games 1, 4, 5, and 6. Without actually listing the various series between team A and B, find the exact number of different sequences of games possible. Be able to explain why your answer is correct.
5! / (3! 2!) for each A and B, for a total of 10.