Book sales. A bookstore in your city claims that fiction books have more sales in the second half of the year than in the first half. Average monthly sales for a sample of fiction books sold at bookstores throughout the city over a period of one year provides the following data for gross earnings

(in dollars) during the two halves of the year.

Year N Mean StDev Minimum Maximum First half 194 17947 2047 10931 23454 Second half 305 38832 1259 22343 53347

a) How much difference is there between the mean gross earning of fiction books (in dollars) between the two halves of the year? (Assume that this time frame represents typical book sales in the city.)

b) Construct and interpret a 95% confidence interval for the difference between the average monthly gross earnings for the first and second half of the year.

c) Suggest a factor that might have inf luenced the sales of the fiction books during the first half of the year.