Jennifer Dahl, supervisor of the Circle O discount chain, would like to forecast the time it takes to check out a customer. She decides to use the following independent variables: number of purchased items and total amount of the purchase. She collects data for a sample of 18 customers, shown in Table P-8.

a. Determine the best regression equation.
b. When an additional item is purchased, what is the average increase in the checkout time?
c. Compute the residual for customer 18.
d. Compute the standard error of the estimate.
e. Interpret part d in terms of the variables used in this problem.
f. Compute a forecast of the checkout time if a customer purchases 14 items that amount to $70.
g. Compute a 95% interval forecast for your prediction in part f.
h. What should Jennifer conclude?

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