In testing the difference between two population means using two independent samples, we use the pooled variance in estimating the standard error of the sampling distribution of the sample mean difference 1 2 if the:

A) sample sizes are both large

B) populations are normal with equal variances

C) populations are nonnormal with unequal variances

D). populations are normal with unequal variances

Small computing center has found that the number of jobs submitted per day to its computers has a distribution that is approximately mound-shaped and symmetric, with a mean of 64 jobs and a standard deviation of 6. Where do we expect most (approximately 95%) of the distribution to fall?

A) between 46 and 82 jobs per day

B) between 76 and 82 jobs per day

C) between 52 and 76 jobs per day

D) between 58 and 70 jobs per day