Three friends check into a motel for the night and the clerk tells them the bill is $30, payable in advance. So, they each pay the clerk $10 and go to their room. A few minutes later, the clerk realizes he has made an error and overcharged the trio by $5.
He asks the bellhop to return $5 to the 3 friends who had just checked in.
The bellhop sees this as an opportunity to make $2 as he reasons that the three friends would have a tough time dividing $5 evenly among them; so he decides to tell them that the clerk made a mistake of only $3, giving a dollar back to each of the friends. He pockets the leftover $2 and goes home for the day!
Now, each of the three friends gets a dollar back, thus they each paid $9 for the room which is a total of $27 for the night.
We know the bellhop pocketed $2 and adding that to the $27, you get $29, not $30 which was originally spent.
Where did the other dollar go?