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 P.M., what is the probability that he misses part of the sport report if he waits until grading is done before turning on the TV?

A First Course in Probability (10th Edition)
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ISBN:9780134753119
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Chapter1: Combinatorial Analysis
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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 P.M., what is the probability that he misses part of the
sport report if he waits until grading is done before turning on the TV?
Transcribed Image Text: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 P.M., what is the probability that he misses part of the sport report if he waits until grading is done before turning on the TV?
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