Numbers every store owner and merchandiser needs: sale prices, margins, deals, tests and tax.
Work out the sale price, the discount or the regular price from the other two - in percent or dollars.
From any two of cost, price, margin or markup, get the rest - and stop mixing up margin and markup.
20% off, $15 off or buy two get one free? See which deal is really cheapest for your cart.
Is version B really better? Get conversion rates, lift and statistical significance.
Add tax to a price, or take it out of a price that already includes it - any rate, sales tax or VAT.