Hi, Why is u1-u2 = 0 in this case? The hypothesis is that u1-u2 <= 0, not u1-u2 == 0. Thanks.

More info needed…

Look at the solution. the u1-u2 portion of the equation equals to 0…

tstte, not all those writing to help us here are candidates - some are already charter holders, so they don’t have the textbooks, but are willing to share their own time to help us. Now, if you check the explanations provided at the back of the book, at point B, it says that “based on the samples it is reasonable to assume that population variances are equal" – although as you said the null is u1-u2<=0.

o I must have missed that line. I’ll check it out again tonight. Thanks!

Why is it considered reasonable? Is it because the standard deviation of the two samples are within 0.01? Thanks.