PERENCANAAN & PENGENDALIAN PRODUK

During the past 8 quarters, the Port of Baltimore has unloaded large quantities of grain. (a = .10). The first quarter forecast was 175. Find the forecast for the 9th quarter.

Quarter Actual

1 180
2 168
3 159
4 175
5 190

6 205

7 180

8 182

9 ?

Jawab:

Cara 1:

Ft = Ft-1 + a(At-1 - Ft-1)

Tabel Hasil Perhitungan

Quarter	Actual	Forecast
1 2 3 4 5 6 7 8 9	180 168 159 175 190 205 180 182 ?	175 175,5 174,75 173,175 173,36 173,02 178,02 178,22 178.6

Contoh Perhitungan:

1. Ft2 = Ft(2-1) + a(At (2-1) – Ft(2-1))

= Ft1 + a(At1 - Ft1)

= 175 + 0,1 ( 180 – 175)

= 175,5

2. Ft3 = Ft(3-1) + a(At (3-1) – Ft(3-1))

= Ft2 + a(At2 – Ft2)

= 175,5 + 0,1 ( 168 – 175,5)

= 174,5

Demikikan hingga diperoleh nlai Ft8, yaitu 178,22

3. Ft9 = Ft(9-1) + a(At (9-1) – Ft(9-1))

= Ft8 + a(At8 – Ft8)

= 178,22 + 0,1 ( 182 – 178,22)

= 178,6

Jadi, nilai ramalan untuk quarter ke-9 adalah sebesar 178,6.

Cara 2:

Ft = aAt - 1 + a(1-a)At - 2 + a(1- a)²·At - 3 + a(1- a)³At - 4 + ...

+ a(1- a)^t-1·A0

= 0,1.182 + 0,1(1-0,1).180 + 0,1(1-0,1)².205 + 0,1(1-0,1)³.190 +…..+ 0,1(1-0,1)⁷.180

= 103,263

Jadi, nilai ramalan untuk quarter ke-9 adalah sebesar 103,263.