The sales of the last $12$ months in a computer company occur immediately. Respond by giving procedures and answers.

MONTH $/$ SALES $($millions of $$)$

January $20$th

February $24$

March $29$

April $32$

May $37$

June $47$

July $53$

August $62$

September $64$

October $36$

November $23$

December $29$

a$)$ Use a three$-$month moving average to forecast sales for January of the following year.

b$)$ Use a four$-$month moving average to forecast next year's January sales.

c$)$ Compare the performance of the two methods using the mean absolute deviation as the performance criterion. What method would you recommend?

d$)$ Compare the performance of the two methods using the mean percentage error as the performance criterion. What method would you recommend?