An educator wants to determine the difference between the proportion of males and females who have completed 4 or more years of college. What sample size should be obtained if she wishes the estimate to be within 2 percentage points with 90% confidence, assuming that
(a) she uses the 1999 estimates of 27.5% male and 23.1% female from the U.S. Census Bureau?
(b) she does not use any prior estimates?