Since May of 2005, the purchase manager at department store has been using the 4period moving average to forecast sales in next months. Sales data for months of January through July are given in the table below.
Month

Sales

Jan

65

Feb

65

Mar

41

Apr

50

May

63

June

38

Jul

72

Evaluate the mean absolute deviation (or MAD) for fourperiod moving average forecasts. The forecast values are computed with accuracy of two decimal digits. Identify the MAD as an entire number by rounding.