Total sleep time of college students. In Example 7.1, the total sleep time per night among college students was approximately Normally distributed with mean μ = 7.02 hours and standard deviation σ = 1.15 hours (page 360). Suppose that you plan to take an SRS of size n = 400 and compute the average total sleep time.
(a) What is the standard deviation for the average time?
(b) Use the 95 part of the 68-95-99.7 rule to describe the variability of this sample mean.
(c) What is the probability that your average will be below 6.9 hours?