Visually impaired students. The Journal of Visual Impairment & Blindness (May–June 1997) published a study of the lifestyles of visually impaired students. Using diaries, the students kept track of several variables, including number of hours of sleep obtained in a typical day.

These visually impaired students had a mean of 9.06 hours and a standard deviation of 2.11 hours. Assume that the distribution of the number of hours of sleep for this group of students is approximately normal.

a. Find the probability that a visually impaired student obtains less than 6 hours of sleep on a typical day.

b. Find the probability that a visually impaired student gets between 8 and 10 hours of sleep on a typical day.

c. Twenty percent of all visually impaired students obtain less than how many hours of sleep on a typical day?