Four numbers, one answer, every operation allowed
Twenty-four
Turn four cards and make exactly 24 using all four, in any order, with any operations. The purest order-of-operations drill there is, and it plays in thirty seconds.
- Players
- 2 to 6
- Time
- As long as you like
- Ages
- 10 and up
What you need
- A standard deck of cards with the picture cards removed
How to play
- Strip the deck. Take out the jacks, queens and kings. Aces count as one.
- Turn four cards. Turn four cards face up in the middle where everyone can see them.
- Race to 24. Everyone works at once. You must use all four numbers, each exactly once, and you may add, subtract, multiply and divide in any order and group them however you like.
- Claim it. The first player to see a solution says 'twenty-four' and then shows it. If it works they take the four cards. If it does not, they sit out until the next turn.
- Keep going. Turn four more. The player with the most cards when the deck runs out wins.
The maths in it
It teaches that operations are tools to be chosen rather than instructions to be obeyed. 3, 3, 8, 8 is famously hard — the answer needs division and a fraction — and the moment a child finds it is the moment they stop thinking of division as the last resort.
Making it fit the child
Easier: Use three cards and aim for 12. Allow a pass if nobody sees it within a minute; not every set of four has a solution, which is worth saying out loud so a child does not conclude they are stupid.
Harder: Insist the solution is spoken as one sentence before the cards are touched, so it has to be held in the head complete.