University students average 7.2 hours of sleep per night with a standard deviation of 40 minutes. If the amount of sleep is normally distributed, what proportion of university students sleep for more than 8 hours

Answer 1

8 hr is 48 min above the mean ... this is 48/40 s.d. (1.2 z-score)

go to a z-score table to find the % of the population above 1.2