Excel formula for reverse percentage calculation

Question

I have a calculation which I am unable to crack.

Lets say my Cost Price is 300. I want to sell the item at No Profit or No Loss. My total commission/expenses will be

Answer 1

I was looking for a similar equation/formula, but then I built it in Excel.

So if you have, say, an item with

CostPrice = 200

Then you add a ProfitMargin = 20% so the

SellPrice = 200 + 20% = 240

Then the reverse equation for this will be

CostPrice = ( SellingPrice * 100 ) / ( ProfitMargin + 100 )

// In your case it should be
CostPrice = ( 390 * 100 ) / ( 30 + 100 )
          = 300

See it in action :)