Blood of Accounting

Cost of Goods sold as per FIFO method is different. ( Unit first purchase* purchase price) . 

Oping Stock + Purchase + Direct  Expense  -  Sales + Direct income + Closing Stock  =  Gross profit 

Gross Profit  + Indirect  Income - Indirect  Expenses = Net Profit 

Simple, closing stock = opening stock. Or else 

If opening stock is ten inr, purchases is ten inr, sales is hundred inr, GP is eighty inr, closing stock is ten inr, depreciation is ten. Then 

Cogs is twenty. GP is eighty inr

So mathematically you can define it as 

Sales-GP-Purchases-Depreciation+closing stock= ten opening stock. This is one way I have defined it. There are other ways you can define it. This is funny. So technicians defined this legally as 

Cogs+closing inventory-purchases-depreciation. This is a website version. If we test it now, previously our cos is twenty so , ten inr is our opening stock.  it works properly. cheers.

So there can be another way you can define it using maths 

If you use my formula in an interview, you'll fail. If you use text formula, you'll pass. 

That's why B.com people never got far away.