Mary Marsh, Head Aerobic Instructor at Tuff-It-Out Fitness Centers, Wanted

Mary Marsh, head aerobic instructor at Tuff-it-Out Fitness Centers, wanted to estimate the proportion of all 19-39 year olds who aerobically exercise at least once each week. Mary would like the estimate to be within plus or minus 3 percentage points of the mean and she would like to have 90 percent confidence (z=1.645) in her results. Use this information to answer the next three questions.
-Suppose in the previous problem that a 99 percent confidence interval (z=3) were desired. The required sample size is

A) 24.
B) 240.
C) 1,600.
D) 2,400.
E) 3,200.