Three ppl walk into a supermarket. They buy an item that costs £30. Since they have £10 each, they each contribute to the total of the sale price. As they walk to the cashier, she notifies them that there’s a mistake and in reality the item costs £25. She hands them their £5. Since they can’t equally divide the £5 note, they decide to share £3 amongst them and hand the £2 as a gift to the cashier. Since they each receive a quid back, each pay £9 for the item. So, £9 x 3 = £27. Adding the £2 the cashier has equals £29. Where did the £1 go???