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:

MonthError$1-72-3314651365718-39-1310-211412713814315216-417-418-719-420-1$

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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 each month using exponential smoothing with $=\mathrm{.}2.$

Note: 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 $2$s limits$.$

Note: Round your intermediate calculations to $3$ decimal places and final answer to $2$ decimal places.

b$-2.$ What can you conclude?

multiple choice

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$.$