Two samples are selected from the same population. For each of the following, calculate how much difference is expected, on average, between the two sample means.
a. One sample has n = 4, the second has n = 6, and the pooled variance is 60.
b. One sample has n = 12, the second has n = 15, and the pooled variance is 60.
c. In part b, the sample sizes are larger, but the pooled variance is unchanged. How does larger sample size affect the magnitude of the standard error for the sample mean difference?