Three people check into a hotel. They pay $60 as the rent of the room. After they check-in, the manager realize that the rent for the room is $55. So, he gives $5 to the bellboy and asks him to give it to them. The bellboy thinks that it will be difficult for the three people to share $5 among them and seeking the personal benefit, he pockets $2 and gives the remaining $3 to them.
Now, each person paid $20 and got back $1. In this manner, each of them paid just $19 which totals to the amount of $57. The bellboy has $2 with him and adding them, we get $59. So where is the remaining $1?
This is a classic riddle. The trick is to be careful how you are adding things. They paid $60 originally and received back $3. So in this manner, they have paid just $57 for the rent. Out of this $57, $55 are with the manager and $2 are with the bellboy.