7. In the independent-measures hypothesis test, the difference between two sample means is used to test a hypothesis about the difference between two population means. The sample mean difference is not expected to be exactly equal to the population mean difference, and the estimated standard error measures how much discrepancy is reasonable to expect on average. For each of the following situations, compute the estimated standard error for the sample mean difference.

a. First sample has n = 8 and 55 = 416; second sample has n = 8 and 55 = 480.

b. First sample has n = 8 and 55 = 170; second sample has n = 4 and 55 = 70.