Three men go to a restaurant. They order some food. After they have finished, they ask for the bill. The bill was 30$ . They pay the bill and leave the restaurant.
As soon as they leave, the manager find out that there was a miscalculation and that they actually had to pay 25$ .
He calls the waiter, give him the extra 5\$, and ask him to pass this money back to men. The waiter leaves the restaurant with 5\$ , but he put 2\$ in his pocket and give each man 1\$.
Each man payed $ 10\$-1\$ = 9\$ $.
Three man payed $ 9\$*3=27\$ $.
The waiter has $ 2\$ $
The total is $ 27\$ + 2\$ = 29\$ $
Where is the last $ 1\$ $?