[Mylenka]

Here's one for you:

Three men are watching a football match on TV. Suddenly, they get hungry and decide to order a pizza. Each of them gives 10$ so it's 30$, right? About 20 minutes later comes a pizza deliverer, gives men a pizza and takes that 30$ with him. In the office, his boss tells him that he made a mistake! The pizza is 25$, not 30$ so he has to go ang give those 5$ back. As the deliverer is moving back to the house, he realises that there's no way to part 5$ to 3 people and decides to take 2$ of a tip and gives the rest to the men so each of them gets 1$ back. That means, if each of them had given 10$ and got 1$ back it's the same as he had given 9$ before.
Now look --> 3x9$=27$, 27$+2$ of the tip=29$, not 30. So where is the vanishing dollar? ;3

Have fun with it =D