20. In this problem, you are to test the validity of your forecasting model. Here are the fore- casts for a model you have been using and the actual demands that occurred: Forecasting Chapter 18 Week Forecast Actual 1 800 900 2 850 1,000 1,050 3 950 4 950 900 5 1,000 900 6 975 1,100 20. In this problem, you are to test the validity of your forecasting model. Here are the fore- casts for a model you have been using and the actual demands that occurred: Week Actual Forecast 800 1 900 2 850 3 950 4 950 1,000 1,050 900 900 1,100 1,000 975 6 Use the method stated in the text to compute MAD and the tracking signal. Then, decide whether the forecasting model you have been using is giving reasonable results