16. Sleeping During the Full Moon. A study found that subjects slept on average 20 minutes less on nights of the full moon than otherwise.²¹ Other researchers disagree and are interested in testing whether the mean difference in sleep is less than 20 minutes. A random sample of 100 subjects showed that they slept, on average, 10 minutes less on nights of the full moon than otherwise. Assume the population standard deviation is 15 minutes. Perform the appropriate hypothesis test using level of significance .