3 guys go to London for the weekend and book into a cheap hotel-the receptionist tells them the room will cost 30 pounds,so they each pay a tenner each and go to their room.
Ten minutes later,the receptionist realises she has overcharged them and that the actual room cost is £25,so she calls the porter,gives him five pound coins and tells him to take the refund up to the room and give them it.
On the way upstairs,the porter pockets 2 quid for himself and refunds the 3 men one pound each.
So this means they have each paid £9 for the room-3x9=27,plus the £2 the porter took=£29.
so where is the other pound?