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?