Question

The managers of Mercury Mufflers find that the time t (in minutes) required for a worker to replace a muffler varies. Over a period of a year, they collected the following data:

t	Relative Frequency
20	10%
30	50%
40	30%
50	10%

a. Calculate the mean and standard deviation of the replacement time t.

b. They plan to do 50 mufflers with 4 men in a day and hope to finish them all between 9 a.m. and 5 p.m. What proportion of the days will they fail to finish on time?

c. What crucial assumption did you implicitly make? Suggest some circumstances where it would be seriously violated. Then how would the correct answer be different?

I already completed part A and got the mean aas 34 and standard deviation at 8. I just don't know how to start part B.

Answer 1