The bag of cards

Kai, Mia and Tom win a bag of rare trading cards at a tournament. They agree to share it like this: Kai gets half the cards, Mia gets a third and Tom gets a ninth.

But the number of cards will not divide by 2, by 3 or by 9. They argue until the shop owner, Mrs Okafor, puts one of her own cards on the pile. 'Now try,' she says.

Kai takes half, Mia takes a third and Tom takes a ninth. Everyone gets whole cards, and one card is still left on the table. Mrs Okafor picks up her card and goes back to the till.