A survey of the mean number of cents off that coupons give was conducted by randomly surveying one coupon per page from the coupon sections of a recent San Jose Mercury News. The following data were collected: 20; 80; 55; 65; 30; 55; 40; 40; 30; 55; $1.50; 40; 65; 40. Assume the underlying distribution is approximately normal

x =

s_{x} =

n =

n − 1 =

Which distribution should you use for this problem? (Enter your answer in the form z or t_{df} where df is the degrees of freedom.)