A certain predicting method would procuse forecast show in the bottom row for last four months, as compared to actual demand in same four months as given in the middle row. Determine the MAD (Mean Absolute deviation)?
Month -4 -3 -2 -1
Actual Demand 105 100 95 90
Forecast 102 101 110 111
a. 102.5
b. 97
c. 10
d. 4