A 2003 study found that medical student’s mean number of hours worked in a week is 81.7 ...

     A 2003   study found that medical student’s mean number of hours worked in a week is   81.7. Suppose the number of hours worked per week by medical residents is   approximately normally distributed with a standard deviation of 6.9 hours.   What is the probability that a randomly selected medical resident works more   than 80 hours in a week? What is the probability that a randomly selected   medical resident works more than 100 hours in a week? What is the probability   that a randomly selected medical resident works less than 60 hours in a week?