Twenty observations on etch uniformity on silicon wafers

Twenty observations on etch uniformity on silicon wafers are taken during a qualification experiment for a plasma etcher. The data are as follows:

(a) Construct a 95 percent confidence interval estimate of σ²

(b) Test the hypothesis that σ² = 1.0. Use α = 0.05. What are your conclusions?

(c) Discuss the normality assumption and its role in this problem.

(d) Check normality by constructing a normal probability plot. What are your conclusions?