In semiconductor manufacturing, wet chemical etching is often used to remove silicon from the backs of wafers prior to metalization. The etch rate is an important characteristic in this process and known to follow a normal distribution. Two different etching solutions have been compared, using two random samples of 10 wafers for each solution. Assume the variances are equal. The etch rates are as follows (in mils per minute): Solution 1 Solution 2
9.9 10.6 10.5 10.2
9.4 10.3 10.6 10.2
9.3 10.0 10.7 10.7
9.6 10.3 10.4 10.4
10.2 10.1 10.5 10.3

Required:
a. Construct normal probability plots for the two samples. Do these plots provide support for the assumptions of normality and equal variances? Write a practical interpretation for these plots.
b. Do the data support the claim that the mean etch rate is the same for both solutions? In reaching your conclusions, use α = 0.05 and assume that both population variances are equal. Calculate a P-value.
c. Find a 95% confidence interval on the difference in mean etch rates