Using diaries for many weeks, a study on the lifestyles of visually impaired students was conducted. The students kept track of many lifestyle variables including how many hours of sleep obtained on a typical day. Researchers found that visually impaired students averaged 9.21 hours of sleep, with a standard deviation of 2.97 hours. Assume that the number of hours of sleep for these visually impaired students is normally distributed.

(a) What is the probability that a visually impaired student gets less than 6.8 hours of sleep?

answer:

(b) What is the probability that a visually impaired student gets between 6.9 and 9.41 hours of sleep?

answer:

(c) Twenty percent of students get less than how many hours of sleep on a typical day?

answer: hours