In a recent study, the percentage of high school students who have smoked a cigarette in the last 30 days was 15.7%. A principal wanted to estimate this proportion at her school, so she asked 180 students the same question. 21 students said yes.

a. verify the conditions have been met for calculating a confidence interval for p, the proportion of students at this school who have smoked a cigarette in the last 30 days.

b. calculate a 95% confidence interval for p