The manager of a retail store gets a summary of the average daily sales for the prior month. The manager uses these data to monitor the performance of advertising and the employees. The store has been...

The manager of a retail store gets a summary of the average daily sales for the prior month. The manager uses these data to monitor the performance of advertising and the employees. The store has been open for several years and has a steady history of solid business. In May, the manager learns that sales in April were below average.

a. Should it be a surprise to find that sales in a month are below average?14

b. Before the manager concludes there’s a problem, what plots would clarify the situation?15

c. Sales at this store average $150,000 daily with standard deviation $20,000. If sales were $90,000 in April, what is the z-score for sales in April?16 d. Should the manager be concerned about the level of sales in April?17