7. The general manager for Gordon's Self Service Gasoline is interested in estimating the mean number of gallons of gasoline that are purchased by customers in a single purchase. He would like his estimate to be within 0.5 gallons and he would like the estimate to be at the 99% confidence level. Past studies have shown that the standard deviation for the amount of gas purchased is 4 gallons.

a) What is the minimum required sample size to achieve these results?

b) State the units for part (a). In other words what will you sample?