An appliance manufacturer offers maintenance contracts on its major appliances. A manager wants to know what fraction of buyers of the company's convection ovens are buying the maintenance contract with the oven. From a random sample of 120 sales slips, 31 of the oven buyers opted for the contract.

a. The proportion of customers who buy the contract along with their oven is estimated as.

b. Calculate a standard error for the estimate in part a.

c. Calculate a 95% interval estimate for the true proportion of customers who buy the contract along with their oven

d. Interpret the interval in part c