The classified department of a monthly magazine has used a combination of quantitative and qualitative methods to forecast sales of advertising space. Results over a 20 -month period are as follows: Click here for the Excel Data File a. Compute a tracking signal for months 11 through 20 . To do so, compute an initial value of MAD for month 11 , and then update it for each month using exponential smoothing with a=.4. (Leave no cells blank - be certain to enter " 0 " wherever required. Negative values should be indicated by a minus sign. Round your intermediate calculations and final answers to 3 decimal places.) b-1. Using the first half of the data, construct a control chart with 2s limits. (Round your intermediate calculations to 3 decimal places and final answer to 2 decimal places.) b-2. What can you conclude? Only the error for month 9 is outside of the limits. Only the error for month 5 is outside of the limits. All errors are within these limits