There is a 0.1755 probability that a best-of-seven contest will last four games, a 0.1836 probability that it will last five games, a 0.2073 probability that it will last six games, and a 0.4336 probability that it will last seven games. Verify that this is a probability distribution. Find its mean and standard deviation. Is it unusual for a team to "sweep" by winning in four games?