The Economics Department Secretary Wants to Estimate the Average Number $\bar { x }$

Short Answer

The economics department secretary wants to estimate the average number of bottled drinks sold each day out of the vending machine.Similar vending machine sales have a standard deviation of 9 bottles per day.She wants to be 95-percent confident that the estimate, $\bar { x }$ ,obtained is within 3 bottles of the true mean $\mu$ .How large a sample is needed?