Since May of 2005, the purchase manager at a department store has been using a 4-period moving average to forecast sales in upcoming months. Sales data for the months of January through July are given in the table below.
Month Sales
Jan 65
Feb 65
Mar 41
Apr 50
May 63
Jun 38
Jul 72
Compute the mean absolute deviation (MAD) for the four-period moving average forecasts. The forecast values are calculated with an accuracy of two decimal digits. Specify the MAD as a whole number by rounding.