According to the Department of Education the mean number of hours college students spend studying each week follows a normal distribution with a mean of 20 hours and standard deviation of 9 hours....

According to the Department of Education the mean number of hours college students spend studying each week follows a normal distribution with a mean of 20 hours and standard deviation of 9 hours.

• What ‘hours of study’ represents the 90^th
  percentile?

• What ‘hours of study’ represents the 15^th
  percentile?