Sleep time: In a sample of 87 young adults, the average time per day spent in bed asleep was 7.06 hours. Assume the population standard deviation is 1.11 hours.

a. Construct a 99% confidence interval for the mean time spent in bed asleep.

b. Some health experts recommend that people get 8 hours or more of sleep per night. Based on the confidence interval, is it reasonable to believe that the mean number of hours of sleep for young adults is 8 or more? Explain.

c. How large would the sample have to be so that a 99% confidence interval would have a margin of error of 0.1?

Source: Behavioral Medicine 27:71–76