The daily sleep duration among college students is normally distributed with a mean of 8.13 and standard deviation of 1.87. If you plan to take an SRS of size 60, what is the mean of your average time? The daily sleep duration among college students is normally distributed with a mean of 8.13 and standard deviation of 1.87. If you plan to take an SRS of size 60, what is the standard deviation of your average sleep time? The daily sleep duration among college students is normally distributed with a mean of 8.13 and standard deviation of 1.87. You want to use a sample size such that 95% of the averages fall within +15 minutes (.25 of an hour) of the true mean of 8.13. Determine the smallest number of students you need to sample.