a$)$ Use exponential smoothing, first with a smoothing constant of $6$ and then with one of $9,$ to develop forecasts for years $2$ through $6.$

b$)$ Use a $3-$year moving average to forecast demand in years $4,5,$ and $6.$

c$)$ Use the trend$-$projection method to forecast demand in years $1$ through $6.$

d$)$ With MAD as the criterion, which of the four forecasting methods is best?

$4\mathrm{.}6$

The monthly sales for Yazici Batteries, Inc., were as

follows:

$\backslash$table$[[$Month$,$SAIES$],[$January$,20],[$February$,21],[$March$,15],[$April$,14],[$May$,13],[$June i$.,16],[$July$,17],[$August$,18],[$September$,20],[$October$,20],[$November$,21],[$December$,23]]$

a$)$ Plot the monthly sales data.

b$)$ Forecast January sales using each of the following:

i$)$ Naive method.

ii$)$ A $3-$month moving average.

iii$)$ A $6-$month weighted average using $\mathrm{.}1,\mathrm{.}1,\mathrm{.}1,\mathrm{.}2,\mathrm{.}2,$ and $\mathrm{.}3,$ with the heaviest weights applied to the most recent months.

iv$)$ Exponential smoothing using an $=\mathrm{.}3$ and a September forecast of $18.$

v$)$ A trend projection.

c$)$ With the data given, which method would allow you to forecast next March's sales?