In a recent study of animal sleep times at the zoo, the mean amount of sleep per night is 6.3 hours with a standard deviation of 2.1. If 23 animals are selected, find the probability that the mean sleep time per night is greater than 8 hours.

An automobile assembly line operation has a scheduled mean completion time, μ, of 12 minutes. the standard deviation of completion times is 1.6 minutes. it is claimed that, under new management, the mean completion time has decreased. to test this claim, a random sample of 33 completion times under new management was taken. the sample had a mean of 11.2 minutes. assume that the population is normally distributed. can we support, at the 0.05 level of significance, the claim that the mean completion time has decreased under new management? assume that the standard deviation of completion times has not changed.