"Rick Rothstein \(MVP - VB\)" wrote...
I'm an engineer-type person, not a business-type person; but, as I
understand the terms, I think you want this...

=A1*(1+B1)

where A1 holds the price you paid for the item and B1 holds the
margin as a fraction (0.30 for 30%).
....

That's mark-up. Margin is expressed as a percentage of revenue, not
cost of goods sold. Given your set-up, the correct formula is

=A1/(1-B1)

Another way to think about it: you can't have more than 100% margin,
but you can have more than 100% mark-up.