In a study of government financial aid for college students, it becomes necessary to estimate the percentage of full-time college students who earn a bachelor's degree in four years or less.

Using a 0.02 margin of error and 90% confidence level, find the sample size needed to estimate that percentage with the following assumptions:

a) Nothing is known about the percentage estimated.

b) Prior studies have shown that about 40% of full-time students earn bachelor's degrees in four years or less.