Quick! The Zombies are coming and need to find the right brains to eat!
Students sort the cards onto the brains, deciding whether each number is prime or composite. As they place the card, they must explain how they know the number is prime or composite. (You should decide which set of brains to use — the ones with the definitions or the ones without.)
When students are very comfortable with the material, you could add a timer to the activity and challenge them to sort the cards as quickly as possible (without explaining their reasoning). The person who places them the quickest with the most correct is the winner (or the lead Zombie, if you prefer!).
Included are 56 cards of numbers under 100 to sort, 2 sets of brain mats (1 set labeled with Prime/Composite and 1 set also labeled with the definitions of prime and composite), and an answer key so students can check their work.
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Thanks for looking! :)