Develop a double exponential smoothing model using smoothing constants a  0.20 and b  0.40. As starting values, use the least squares trend line slope and intercept values.

a. Compute the MAD for this model.

b. Plot the forecast values against the actual data.

c. Use the same starting values but try different smoothing constants [say,

(a,

b)  (0.10, 0.50),

(0.30, 0.30), and (0.40, 0.20)] in an effort to reduce the MAD value.