A machine produces metal rods used in an automobile suspension system. A random sample of 15 rods is selected, and the diameter is measured. The resulting data (in millimeters) are as follows:

8.20 8.25 8.18 8.25 8.22 8.20 8.28 8.28 8.18 8.24 8.25 8.25 8.17 8.26 8.22

(a) Check the assumption of normality for rod diameter.

(b) Calculate a 99% two-sided confidence interval on mean rod diameter.

(c) Calculate a 99% upper confidence bound on the mean.

(d) Compare this bound with upper bound of the two-sided confidence interval and discuss why they are different.