JPSem

Begin Inventory + Purchases - End Inventory = COGS.

Begin Inventory and Purchases is the same.
Put numbers
Begin Inv = 200
Purchases = 100
End Inventory = 150 say
COGS = 200 + 100 - 150 = 150

Now say there was the writedown - and End Inventory became 100

Applying the same to the above -> COGS = 200

CP