7.11. The College Alcohol Study at the Harvard School of Public Health has interviewed random samples of students at 4-year colleges several times since 1993. Of the students who reported drinking alcohol, the percentage who reported that drinking "to get drunk" is an important reason for drinking was 39.9% of 12,708 students in 1993 and 48.2% of8783 students in 2001.6 For comparing results in 1993 and 2001:

(a) Show thatthe standard error for the estimated difference between the corresponding population proportions in 2001 and in 1993 equals 0.0069.

(b) Show that the 95% confidence interval for the difference is (0.07, 0.10). Interpret.