Ithacaman - Profit is the amount of your revenue that exceeds your expense. Profit here is calculated based on what you sell for. If you pay $50, sell for $100 (100% markup), your profit is $50 -- 50% of your revenue.
GregSy - So much for disdain of hairsplitting. Would you say your profit % is infinite? One could think of an infinite number of examples of selling something that supposedly cost nothing. I can't tell you how, but trust me that business/tax accounting rules cover them and yet preserve the definition of profit.
