We illustrate how to use JMP to do a two sample t-test with the example on Page 395 of your textbook involving the Armor-Plating Experiment. This is the JMP table with the data:
We proceed as follows:
If we can assume that the two populations of alloys have equal variances we proceed as follows:
Notice that the P-value is <.0001 so we reject the hypothesis of equal means at the at the alpha levels of .05 and .01
If we cannot assume that the two populations of alloys have equal variances we proceed as follows:
Notice that even if we don't assume equal variances the P-value is <.0002 so we again reject the hypothesis of equal means at the at the alpha levels of .05 and .01. Welch test is not the test given in the textbook for dealing with the case where the variances are not equal.