There are 40 students in an elementary statistics class. On the basis of years of experience, the instructor knows that the time needed to grade a randomly chosen exam paper is a random variable with an expected value of 6 minutes and a standard deviation of 6 minutes.
(a) If grading times are independent and the instructor begins grading at 6:50PM and grades continuously, what is the (approximate) probability that he is nished grading before the 11:00PM TV news begins?
(b) If the sports report begins at 11:10, what is the probability that he misses part of the report if she waits until grading is done before turning on the TV?