My Mrs was asking me this stupid little story thing last night, and wont tell me the answer and its relly annoying me, so any one know the answer to this?!

Right..... 3 blokes walk into a hotel
Ask the women at reception for a room to share
She says yes we have, that will be £30 between you, so they pay £10 each.
They get to there room, then she comes back with5 £1 coins and says they were over charged by £5. (Which makes the room £25)
So she says she will split it, but she cant do it equally,
She then gives them 1 £1 coin each and puts the other 2 £1 coins in her pocket.
Now this is the bit i dont get. Each of the blokes paid £10, got a pound back, Which means they really paid £9.
So £9, times 3 is equal to £27.. Which leaves £1 short because the women put £2 in her pocket. All that equalls £29 ....

So where the hell did the other £1 end up?!

Hope iv explained it right, cus its really annoying and i wonna make her think i worked it out