A supplier received results on the hardness of metal from two different hardening process (1) salt-water quenching and (2) oil quenching. The results are shown in Table 4E.4.

a. Construct a 95% confidence interval on the difference in mean hardness.
b. Construct a 95% confidence interval on the ratio of variances.
c. Does this assumption of normality seem appropriate for this data?
d. What can you conclude?

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Salt Quench Oil Quench 145 150 153 148 141 152 146 154 139 148 152 150 147 155 140 146 158 152 151 143 xs,-147.6, ssoー24.7111, 10 ns,-10, xoo-1494, soo-29.8222,