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. Find the sample size needed to estimate that percentage. Use a 0.05 margin of error, and use a confidence level of 95%.
a. Assume that nothing is known about the percentage to be estimated.
b. Assume that prior studies have shown that about 40% of full-time students earn bachelor's degrees in four years or less.
c. Does the added knowledge in part (b) have much of an effect on the sample size?