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 sl obtained on a typical day Researchers found that visually impaired students averaged 8 88 hours of sleep with a standard deviation of 2 55 hours Assume that the number of hours c sleep for these visually impaired students is normally distributed a What is the probability that a visually impaired student gets less than 6 4 hours of sleep 4 answer b What is the probability that a visually impaired student gets between 6 9 and 8 6 hours of sleep answer c Twenty percent of students get less than how many hours of sleep on a typical day answer hours