:2. Solution. Since (180/900)x100% = 20%, the midpoint of the
confidence interval is 20%. The lower endpoint of a 95%
confidence interval is 2 SE's below its midpoint. The
"bootstrap" estimate for the SE of the total number of students
in a sample of 900 favoring a return to the quarter system is 30
x (the square root of .20 x .80) = 30 x .4 = 12. The SE for the
percentage of such students is (12/900) x 100% = 12/9 = 1.33%.
So the lower endpoint of the confidence interval is 20% - (2 x
1.33%) = 20 - 2.66 = 17.34%, which is closest to 17.4%.