CRA CDs Inc. wants the mean lengths of the "cuts" on a CD to be 150 seconds (2 minutes and 30 seconds). This will allow the disk jockeys to have plenty of time for commercials within each 10-minute segment. Assume the distribution of the length of the cuts follows a normal distribution with a standard deviation of nine seconds. Suppose that we select a sample of 12 cuts from various CDs sold by CRA CDs Inc. Use Appendix B.1 for the z-values.

a. What can we say about the shape of the distribution of the sample mean?

Sample mean (Click to select)

b. What is the standard error of the mean? (Round the final answer to 2 decimal places.)

Standard error of the mean seconds.

c. What percentage of the sample means will be ...