The data for a sample of 80 steel parts, given in Q1 of M9-Assignment.xlsx, shows the reported difference, in inches, between the actual length of the steel part and the specified length of the steel part. For example, a value of minus −0.002 represents a steel part that is 0.002 inch shorter than the specified length.
a) At the 0.01 level of significance, is there evidence that the mean difference is different from 0.0 inches? State the null and alternative hypotheses, use both P-value and critical values for decision making.
b) Do you have to be concerned about the normality assumption?