:4. Solution. 212/400 = .53, so 53% is the center of the
confidence interval. <p>

SE for sum of draws = (.53x.47)^(1/2) x 20 = .5 x 20 = 10
 
SE for sample % = (10/400) x 100% = 2.5% <p>

95% confidence interval = 53% +/  (2 X 2.5%) = 53% +/  5%