additive variations

taskey

evening all

I am a little bit stuck.

i am doing the bpp book for additive variations.

I am working my way through - but this bit i cannot work out.

i have attached a file to this message.

i dont understand how the seasonal variation is worked out. it has given me the formula Y - T but no matter how i work it, i do not get to the figures in the final column.

i thought i could figure this out, but been looking at it for an hour now and am stuck.

Hope some one can help - i am sure they can

Many thanks

Tracy

Pencil

They have worked out the trend by taking a 4 period moving average. This is then used to work out the seasonal variation against the underlying trend. The 4 period average for the Yr 5 Q3 is 650

((600+840+420+720)/4)+((840+420+720+640)/4)/2

the actual sales in Yr 5 Q3 was 420.

Actual - Trend = seasonal variation
420 - 650 = -230

taskey

that makes sense - it was staring me in the face but could not see it

thanks

Tracy