In semiconductor manufacturing, wet chemical etching is often used to remove siliconfrom the backs of wafers prior to metallization. The etch rate is an important characteristic

in this process and known to follow a normal distribution. Two di erent etching solutionshave been compared, using two random samples of 10 wafers for each solution. The observed

etch rates are as follows (in mils per minute):

Solution 19.99.49.39.6 10.2 10.6 10.3 10.0 10.3 10.1

Solution 210.2 10.6 10.7 10.4 10.5 10.0 10.2 10.7 10.4 10.3

a. Calculate the sample mean and standard variance for each sample.

b. Conduct a hypothesis test to test whether the mean etching rates are the same for thetwo different solutions at 0.05 level of significance.

c. What assumptions are required to ensure the validity of the test in (b)?