To use the t-statistic to test for a difference between the means of two populations, what assumptions must be made about the two populations? About the two samples?

What assumption(s) must be made about the two populations? Select all that apply.

a) Both sampled populations must have approximately equal population variances.

b) Both populations must be selected independently of each other.

c) There must be more than 30 samples selected from each population.

d) Both sampled populations must be approximately normally distributed.

What assumption(s) must be made about the two samples? Select all that apply.

a) The samples must be normally distributed.

b) There must be more than 30 samples selected from each population.

c) The samples must be independent of each other.