The manager of a local supermarket wants to know the average amount (in dollars) customers spend at his store on Fridays. He would like to study the buying behavior of each customer who makes a purchase at the store on a typical Friday. However, the manager’s assistant, who is currently enrolled in a managerial statistics course at a local college, urges the manager to save his scarce time and money by studying a sample of customer purchases. The available frame of relevant customer purchases is provided in file P8_51.XLS.

a. Compute the average purchase amount made by the customers included in the given frame.

b. Use Excel to choose a simple random sample of 25 customers from the given frame.

c. Compute the average purchase amount made by the 25 customers in the random sample. Compare this sample mean to the corresponding summary measure obtained in part a.

d. Is the sample mean a good estimate of the overall population mean in this case? Explain why or why not.