Comparing Gasoline Sales Forecasts with Moving Averages and Exponential Smoothing. With a smoothing constant of =0.2, equation (8.7) shows that the forecast for week 13 of the gasoline sales data from Table 8.1 is given by y13=0.2y12+0.8y12. However, the forecast for week 12 is given by y12=0.2y11+0.8y11. Thus, we could combine these two results to show that the forecast for week 13 can be written as y13=0.2y12+0.8(0.2y11+0.8y11)=0.2y12+0.16y11+0.64y^11 a. Making use of the fact that y^11=0.2y10+0.8y10 (and similarly for