Three blind men entered into "Rose Restaurant" for breakfast. After they finished drinking the coffee, Jeff "the ostrich" called the waiter, "the bill, please". The waiter told them they ate the ten bucks meal, Jeff handed him thirty bucks. The waiter went to Rose gives her the money. Rose gave the waiter five bucks and told him, you know my policy, senior citizens and disabled receive a discount of 17%.
So the waiter gave them back five bucks, Jeff handed two bucks to the waiter and each of them got one bucks back. Now let's take off our shoes and do the calculation. Each of them paid nine bucks (Ten minus one) so in total they paid 27 bucks, now two bucks are in the waiter's pocket, now the total is 29 bucks, but they paid 30 bucks so where disappeared one bucks?
Hint:never believe to any given information, check, don't let them cheat you.