A sample of 40 CDs from a student's collection showed a mean length of 52.74 minutes with a standard deviation of 13.21 minutes.
(a) Construct a 95 percent confidence interval for the mean.
(b) Why might the normality assumption be an issue here?
(c) What sample size would be needed to estimate with 95 percent confidence and an error of ±3 minutes? (Data are from a project by statistics students Michael Evatz, Nancy Petack, and Jennifer Skladanowski.)