material costing

4 is not the correct answer. Lifo means that higher priced inventory is used first, leaving earlier, lower priced inventory in stocks.

Yes, you are correct. Sorry for my error. In 3 the WA periodic cost is calculated right over the period, so will always include effects of old, low-priced purchases. The WA cumulative cost is calculated every time there is an addition of goods. However it would be possible for invemtory to have been reduced to zero at somepoint so that the calculation starts anew having only recent relatively expensive purchases in it. Therefore, there is a chance that WA cumulative > WA periodic. Or WA periodic < WA cumulative So it looks as though 3 is right too, as you suggested.