Question: You have just been hired by the marketing division of General Motors to estimate the mean amount of money now being spent on the purchase of new cars in the United States. First use the range rule of thumb to make a rough estimate of the standard deviation of the amounts spent. It is reasonable to assume that typical amounts range from $12,000 to about $70,000. Then use that estimated standard deviation to determine the sample size corresponding to 95% confidence and a $100 margin of error. Is the sample size practical? If not, what should be changed to get a practical sample size?