Using the following time series data, respond to the following items.

a. G raph the time series.

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 quarterly indexes?

f. Forecast sales for future periods 17 through 20.

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Period Quarter Sales Period Quarter Sales 1 1 $ 812 9. 1 $ 965 2 2 920 10 2 844 3 3 1,268 11 3 961 4 4 1,280 12 4 1,160 1 832 13 1 751 791 14 674 7 1,071 15 3 828 1,109 16 4 1,033 3 4