Three friends manager into a hotel for the night and the manager 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 manager realises he has made an error and overcharged the trio by £5. He asks an assistant to return £5 to the 3 friends who had just checked in. The assistant 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 manager made a mistake of only £3, giving a £1 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 £1 back, thus they each paid £9 for the room which is a total of £27 for the night. We know the assistant pocketed £2 and adding that to the £27, you get £29, not £30 which was originally spent. Where did the other £1 go?