Three brothers shopping for a TV walk past a shop and see a TV on sale for £30!. ‘Bargain’ they think only £10 each as they always share the cost equally. So in they go to buy the TV. When they get to the assistant to purchase the TV. He informs them that they are the 1000 customer of the day and they qualify for £5 discount!!!. so the brothers all hand the assistant £10 each, the assistant the goes to hand the brothers there £5 pound change, “oh we share things equally” says one brother, so they all agree to take back £1 each and tip the assistant the remaining £2.
However if the brothers all handed over £10 each but received £1 discount, then they only spent £9 each…so in total they spent 3×9 = £27 and tipped the assistant £2, but 27+2 only equals 29??? were did the other £1 go!!!