Varying cost of inventory

I am a retailer ,i have different categories of inventories with different price,each time i purchase my inventory from the manufacturer,the landing cost differ as a result of the exchange rate ,how can i capture the different costs so as to have it reflect on my P&L in the same way as the attached image.

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@lubos I have the same issue here. I purchased inventory in November 2014 (e.g. $75.00 for a book) at a different price and then purchased some more in January 2015 ($50.00 same book purchased for $75.00 in November) even though the inventory in November had not run out. Can you explain how this will work? Will the purchase price for my November 2014 be overwritten by the new purchase price of stock purchased in January 2015?

Manager basically uses Average costing.

So if you purchase 1 @ 50 + 1 @ 75 when you sell one it will issue it at the average i.e. your cost of goods sold when you sell one would be 62.50. Hope that helps.

It does, thanks @alasdair