In a time series analysis, the additive model is used to forecast sales and the following seasonal variations apply: Quarter 1 2 3 4 Seasonal variation +5.8 -8.4 +10.2 ? The seasonal variation for quarter 4 is: A +7.6 B -8.1 C -7.6 D +8.1
If you sum the variations given you should get 7.6. 5.8+10.2-8.4=7.6. The seasonal variations should add up to zero.Therefore,the final seasonal variation must equal -7.6.