My dad (RIP) used to love to tell this story to people, I still enjoy it myself, and for some reason it popped into my head so thought I'd share!
3 flatmates were in need of a new washing machine, and they found one for sale locally for £30.
They asked their mate John to get it for him, since he had a van.
John duly obliged, and when he went to pick it up, did a deal with the seller and got it for £25.
When he delivered the washing machine back to the flatmates, he explained the deal, and with the £5 change they agreed to accept £1 each back and let John keep £2 for his petrol.
So.............................if the girls therefore paid £9 each, 3 x 9 = £27, plus John's £2 = £29!
Where's the missing pound :)