The percentage of "white area" in a sample of a dark product is used to evalu ate how well a white raw material has been mixed into the product. Using the data from whitearea .txt, which contains samples from two different mixing processes, do the following.
(a) Make a normal probability plot of the residuals and comment on it.
(b) Test to see if white area percentages differ for the two groups using a = 0.10. Explain what your results mean.
(c) Construct a 90% confidence interval for the mean difference in white area percentages and explain what it indicates.