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. Find the probability that a visually impaired student b. obtains less than 6 hours of sleep on a typical day. Find the probability that a visually impaired student gets between 8 and 10 hours of sleep on a typical day. Twenty percent of all visually impaired students obtain less than how many hours of sleep on a typical is day?