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Fifteen is a game for two players that you can play anywhere, anytime. Try it without writing anything down. You take it in turns to choose one of the whole numbers 1 to 9 (and each number can only be chosen once). To win you have to pick 3 numbers that add up to 15.

Can you beat the computer?

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Click on a number to select it.

Can you analyse the structure in the following games and the correspondences between them? Describe the patterns that show they are equivalent games that can be played using equivalent strategies.

We suggest tackling them in the order given.