# Question: a Test the hypothesis that the mean hardness for the

(a) Test the hypothesis that the mean hardness for the saltwater quenching process equals the mean hardness for the oil quenching process. Use a = 0.05 and assume equal variances.

Test H0: 1 2 = 0 vs. H1: 1 2 0. Reject H0 if |t0|>t/2, n1+n2-2.

(b) Assuming that the variances 12 and 22 are equal, construct a 95% confidence interval on the difference in mean hardness.

(c) Construct a 95% confidence interval on the ratio 12 / 22. Does the assumption made earlier of equal variances seem reasonable?

(d) Does the assumption of normality seem appropriate for these data?

Test H0: 1 2 = 0 vs. H1: 1 2 0. Reject H0 if |t0|>t/2, n1+n2-2.

(b) Assuming that the variances 12 and 22 are equal, construct a 95% confidence interval on the difference in mean hardness.

(c) Construct a 95% confidence interval on the ratio 12 / 22. Does the assumption made earlier of equal variances seem reasonable?

(d) Does the assumption of normality seem appropriate for these data?

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