The following data report total, monthly U.S. gasoline sales in millions of dollars from January 2017 to December 2018. (To find the data, go to the site https:// www.census.gov/retail/index.html#mrts, find “Monthly Retail Trade Report,” then select “Time Series/Trend Charts.”)

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 are the monthly indexes?

f. Forecast sales for January, February, March, and April of 2019.

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Sales Sales Year Month ($ millions) Year Month ($ illions) 2017 Jan $34,230 2018 Jan $37,823 2017 Feb 32,572 2018 Feb 35,977 2017 Mar 37,222 2018 Mar 41,248 2017 Apr 37,573 2018 Apr May 41,709 2017 May 39,339 2018 46,649 2017 Jun 38,609 2018 Jun 46,146 2017 Jul 38,397 2018 Jul 46,591 2017 Aug 39,817 2018 Aug Sep 47,433 Sep Oct 2017 39,946 2018 44,185 2017 40,317 2018 Oct 46,942 2017 Nov 38,786 2018 Nov 41.839 2017 Dec 38,646 2018 Dec 38,226