CRA CDs Inc. wants the mean lengths of the cuts on a CD to be 135 seconds

Question:

CRA CDs Inc. wants the mean lengths of the “cuts” on a CD to be 135 seconds (2 minutes and 15 seconds). This will allow the disk jockeys to have plenty of time for commercials within each 10-minute segment. Assume the of the length of the cuts follows the normal with a population standard deviation of 8 seconds. Suppose we select a sample of 16 cuts from various CDs sold by CRA CDs Inc.
a. What can we say about the shape of the of the sample mean?
b. What is the standard error of the mean?
c. What percent of the sample means will be greater than 140 seconds?
d. What percent of the sample means will be greater than 128 seconds?
e. What percent of the sample means will be greater than 128 but less than 140 seconds?

Distribution
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