Find a 95% confidence interval for the proportion of customers who will purchase at least one item

Question:

Find a 95% confidence interval for the proportion of customers who will purchase at least one item if they receive a for 5% off. Repeat for 10% off and for 15% off.

Coupon
A coupon or coupon payment is the annual interest rate paid on a bond, expressed as a percentage of the face value and paid from issue date until maturity. Coupons are usually referred to in terms of the coupon rate (the sum of coupons paid in a...