8-40 a machine produces metal rods used in an auto- mobile suspension system. a random sample of 15 rods is selected, and the diameter is measured. the resulting data (in millimeters) are as follows: 8.24 8.25 8.20 8.23 8.24 8.21 8.26 8.26 8.20 8.25 8.23 8.23 8.19 8.28 8.24 (a) check the assumption of normality for rod diameter. (b) calculate a 95% two-sided confidence interval on mean rod diameter. (c) calculate a 95% upper confidence bound on the mean. compare this bound with the upper bound of the two-sided confidence interval and discuss why they are different.