Problem $4$: $(30$ Marks$)$ Use the demand data that covers a three$-$year period and is

separated by quarters, as indicated below:

ITIS $1$P$97$ Fall $2023$

$3$

a$)$ Use the decomposition method to forecast the demand for each quarter of Year $4$

$($quarter $1,$ quarter $2,$ quarter $3,$ and quarter $4).$ Ensure your Excel file includes the

necessary columns: Seasonal Index, Deseasonalized Forecast $($Forecast for

future periods using the trend line$)$ and Decomposition Forecast. $(25$ Marks$)$

b$)$ Calculate the Mean absolute deviation $($MAD$)$ for the decomposition forecast. $(5$

Marks$)$

Year Quarter Demand

$111100$

$21300$

$31550$

$41450$

$211250$

$21480$

$31780$

$41650$

$311400$

$21670$

$32000$

$4185$