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 first examination paper is a

random variable with an expected value of

6 min and a standard deviation of 6 min.

a. If grading times are independent and the

instructor begins grading at 6:50 p.m. and

grades continuously, what is the (approximate)

probability that he is through grading

before the 11:00 p.m. TV news begins?

b. If the sports report begins at 11:10, what is the

probability that he misses part of the report if

he waits until grading is done before turning

on the TV?