The quarterly sales data (number of copies sold) for a college textbook over the past three years follow:

a. Construct a time series plot. What type of pattern exists in the data?
b. Use an Excel or LINGO model with dummy variables as follows to develop an equation to account for seasonal effects in the data. Qtr1 = 1 if Quarter 1, 0 otherwise; Qtr2 = 1 if Quarter 2, 0 otherwise; Qtr3 = 1 if Quarter 3, 0 otherwise.
c. Compute the quarterly forecasts for next year.
d. Let t = 1 to refer to the observation in quarter 1 of year 1; t = 2 to refer to the observation in quarter 2 of year 1; . . . and t = 12 to refer to the observation in quarter 4 of year 3. Using the dummy variables defined in part (b) and t develop an equation to account for seasonal effects and any linear trend in the time series. Based upon the seasonal effects in the data and linear trend, compute the quarterly forecasts for nextyear.

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Quarter Year Year 2 Year 3 1850 1100 2930 2615 1690 940 2625 2500 1800 2900 2360