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

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 ($ millions) 2017 Jan $51,756 2018 Jan $53,836 2017 Feb 48,335 2018 Feb 50,047 2017 Mar 53,311 2018 Mar 56,455 2017 Apr 52,512 2018 52,836 Apr May 2017 May 54,479 2018 57,035 2017 Jun 52,941 2018 Jun 55,249 2017 Jul 53,859 2018 Jul 55,872 2017 Aug 53,769 2018 Aug 56,173 2017 Sep 52,865 2018 Sep 54,068 2017 Oct 53,296 2018 Oct 55,230 2017 Nov 54,191 2018 Nov 55,807 2017 Dec 57,847 2018 Dec 58,269