A machine produces metal plates used in an automobile suspension system. A random sample of 20 plates is selected, and the thickness is measured. The resulting data (in millimeters) are as follows: 14.86 14.43 14.05 14.00 13.87 14.65
14.31 14.24 14.49 14.15 14.13 14.80
14.34 14.11 13.90 13.75 13.76 14.47
13.84 14.51
(a) Use a Normal Probability Plot to check the assumption of normality for plate thickness. Discuss the plot and your conclusions.
(b) Use a 95% Confidence Interval to determine if it is it believable that the mean plate thickness if 14.15mm?
(c) Is it believable the standard deviation of plate thickness is less than 0.35 mm? Construct the appropriate 99% confidence interval.