$5.[20$ points$]$ Following table shows the sales data of printing paper $($in reams$)$ for the past $12$

weeks at a stationary retailer:

Week $123456789191112$

Sales $761758754756771761767763750766773747$

a$.$ Calculate the forecast sales for week $13$ using three$-$week moving average $[5$ points$]$

b$.$ Forecast sales for week $13$ using the two$-$period weighted moving average method. The

weights are: Wt $=0\mathrm{.}6,$ Wt$-1=0\mathrm{.}4.[5$ points$]$

c$.$ If the actual sales for week $13$ is $760,$ calculate the forecasting error for each method

$($MA and WMA$)$ for week $13.$ State whether forecasted values are under$-$forecasts or

over$-$forecasts. $[5$ points$]$

d$.$ Which forecasting method is more accurate? Explain why. $[5$ points$]$