Independent random samples from two normally distributed populations give the following results:
nx = 10 x-bar = 480 sx = 30
ny = 12 y-bar = 520 sy = 25
a. If we assume that the unknown population variances are equal, find the 90% confidence interval for the difference of population means.
b. If we do not assume that the unknown population variances are equal, find the 90% confidence interval for the difference between population means.