Think of it as, the three people went in only with £30 in their pockets. So there only ever was £30. They give £30 to the receptionist - They now have £0 in their pockets. The receptionist sees his mistake, puts £2 in his pocket and gives £3 back - They now have £3 in their pocket. They have spent £27. £25 has gone to the bill, £2 has gone to the receptionist. Easy. And no Haz, that doesn't work. If he was from heaven, he would point to hell, but if he was from hell, he would point to heaven. And considering you don't know if he is from heaven or hell, you couldn't be sure which way he was pointing. And Dr Nick, there's only one guard? Or would that still work? I know it's fine if there's two guards...