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# Odds and Threes

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### Prime Magic

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Age 7 to 11

Challenge Level

- Game

This is a game for two, three or four players.

You will need a pack of cards with the Jacks, Queens and Kings removed. (Ace is a one)

Deal out two cards to each player.

You can add, subtract, multiply or divide the two numbers to make a whole number, or just put them together to make a 2-digit number.

You score one point for making an odd number, OR a number that can be divided by three.

The player who has the most points after five rounds wins the game.

Example: with these cards you could make the following numbers:

```
46
64
4 + 6 = 10
4 x 6 = 24
6 - 4 = 2
```

But only 24 would score a point because it can be divided by three.

Can you predict as soon as you get your cards if you will be able to make an odd number?

What's the quick way to tell if a number is divisible by 3?

How could you change the game to make it more challenging?

Printable NRICH Roadshow resource.

Place the numbers 1, 2, 3,..., 9 one on each square of a 3 by 3 grid so that all the rows and columns add up to a prime number. How many different solutions can you find?

You can trace over all of the diagonals of a pentagon without lifting your pencil and without going over any more than once. Can the same thing be done with a hexagon or with a heptagon?