It is thought that people paying small purchases (under $25) in a bookstore with cash will spend less than people paying with credit cards. On a Saturday, a random sample of 20 customers who made purchases under $25 and who paid with cash were selected and their purchases averaged. They spent on average $15.45 with a standard deviation of $3.64. The typical credit card purchases (under $25) is $17.30. Construct and interpret a 95% confidence interval and compare to the typical purchase amount.