Required:
What is the value of the mean absolute deviation (MAD) for the forecasting technique whose forecasts for four past periods and the subsequent actual values are given below?
Actual 129 134 138 142
Forecast 136 126 130 146
i) 1.25
ii) 5.25
iii) 2.50
iv) 0.50
v) 6.75
Solve the problem and show all work.