Image via WikipediaNext time you stop at Burger King, check the back of your receipt. You may find instructions for how to earn a FREE whopper with the purchase of fries and a drink. Complete a short, online survey within 48-hours of your visit. At the end of the survey (which really isn't bad), it gives you a code which you write on the back of your receipt. Next time you visit BK, bring your receipt, buy a fry and a drink and they will give you the whopper for free. Nice!