5.16 Sleep duration of college students. In Example 5.4, the daily sleep duration among college students was approximately Normally distributed with mean = 7.13 hours and standard deviation = 1.67 hours. You plan to take an SRS of size n = 60 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?