A text book publishing company has compiled data on total annual sales of its business texts for the preceding 9 years:
year 1 2 3 4 5 6 7 8 9
sale 40.2 44.5 48 52.3 55.8 57.1 62.4 69 73.7
a. using an appropriate model, forecast textbook sales for each of the next five years
b. prepare a control chart for the forecast errors using the original data. Use 2s limits
c. Suppose actual sales for the next five years turns out as follows
year 10 11 12 13 14
sales 77.2 82.1 87.8 90.6 98.9