The following data report total, monthly U.S. book-store sales in millions of dollars fromJanuary 2016 to March 2019. (Go to https://www.census.gov/retail/index.html#mrts,  find “Monthly Retail Trade Report,” then select “Time Series/Trend Charts” to find the data for the total U.S. bookstore sales.)

a. G raph the data.

b. Based on the graph, describe the time series pattern.

c. For this time series, why is forecasting with a seasonally adjusted trend model appropriate?

d. E valuate a seasonally adjusted trend forecasting model. What is the MAD?

e. What is the average monthly trend in book-store sales?

f. What are the monthly indexes? When are book sales the highest? When are book sales the lowest?

g. Predict book sales for the next 9 months.

h. In your judgment, are the forecasts “good”? What disclaimer would you include with your forecast?

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Year Month 2016 2017 2018 2019 $1,428 $1,346 $1,231 $1,104 January February 687 651 669 626 March 679 667 694 645 670 April May 669 689 738 741 746 June 673 664 687 629 July August September 647 661 1,484 1,334 1,324 1,024 957 946 October 675 649 701 November 702 663 728 December 1,216 1,117 1,219