Problem $3-30($Algo$)$

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:

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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 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 $\backslash ($ a$=1\backslash ).$

Note: Leave no cells blank $-$ be certain to enter $"$O$"$ 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 $\backslash (2$ s $\backslash )$ limits$.$

Note: 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 $5$ is outside of the limits$.$

All errors are within these limits$.$

Only the error for month $9$ is outside of the limits$.$