seasonal variation

You have obviously not watch the free lectures on this :-) With multiplicative, since the variations are more or less than 100%, they should add up to 400.

Calculate the seasonally adjusted demand for quarter 2 using the multiplicative model. Quarter Original data Seasonal factor 1 300,000 1.40 2 330,000 0.78 3 360,000 0.92 4 390,000 1.05 The answer is $257,400. Is this right? If we have original data, seasonally adjusted is original data/0.78 = $423,077. Tq sir

Assuming that 'original data' is meaning the actual demand in quarter 2 (which is what I would assume) then the answer is wrong and the correct answer is indeed $423,077. $257,400 would only be correct if $330,000 was the trend figure (and the way the 'original data' is moving does actually suggest that it is meant to be the trend figure). This is a terribly badly worded question if it is worded exactly as you have typed it.