The file Promotiondata.xlsx contains monthly sales (in pounds) of ice cream at a Kroger's supermarket for three years. The file also tells you when promo- tions occurred. Promotions are known to increase sales during the month of the promotion but decrease sales during the month after the promotion. Develop a model that can be used to predict monthly ice cream sales. Hint: Add a term to your model involving the month number; the coefficient of this term will model the trend in ice cream sales.

a. What percentage of variation in ice cream sales is explained by your model?

b. Fill in the blank: 95 percent of forecasts for monthly sales will be accurate within

c. What month appears to be the best for ice cream sales?

d. Describe the trend of ice cream sales.

e. Describe the effect of a promotion on ice cream sales.