Math Trivia!!?

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Three sisters go out for a meal at a restaurant. At the end of the meal, they each give the waiter ten dollars, for a total of thirty dollars. When the waiter looks at the tab, he realized the sum only came to twenty-five dollars. He decides not to show the sisters the tab, but instead pockets two of the dollars for himself and then returns one dollar to each of the sisters, explaining that they'd paid too much.

At the end of the night, then, each of the sister has paid nine dollars (ten minus one), and the waiter has pocketed two. Three times nine is twenty-seven, plus two is twenty-nine. But the sisters originally paid thirty dollars. Where did the extra dollar go?