There is a 0.1253 probability that a best-of-seven contest will last four games, a 0.1711 probability that it will last five games, a 0.2483 probability that it will last six games, and a 0.4553 probability that it will last seven games. Verify that this is a probaility distribution. Find it mean and standard deviation. Is it unusal for a team to "sweep"by winning in four games?