Three guys go to a hotel, wanting a room. The receptionist says it'll be £30, so each man gives him £10, and they go to their room. 10 minutes later, the receptionist (probably blonde or something) realises the room was only £25, so she calls over the bellhop and gives him the £5, sending him to the room the guys were in. Well, the bellhop couldn't work out how to split £5 between three people, so he pocketed £2, and gave each guy £1 back.
So think about it, each guy has now paid £9 (£10 - £1 change), and the bellhop has kept £2 (£5 change - £3 with guys). So three x £9 = £27, + £2 with the bellhop, whos got the other pound?