Prime or composite

💡 How it plays and why it helps

Is 39 prime? Plenty of adults hesitate. Prime or composite asks that kind of question on every card, about one number between 2 and 50, and offers just two answers. The list holds thirty numbers, half prime and half composite, so a number can come back in a round of ten. Your child taps Prime or Composite in this Grade 5 game, and each tap is checked.

A prime number has exactly two factors, 1 and itself; anything with more is composite. The hint asks your child to list the factors, which turns a feeling into a check: 39 has 1, 3, 13 and 39. Odd numbers make up two thirds of the composite half, 9, 15, 21, 25, 27 and more, so the game keeps testing the idea that odd means prime.

Odd numbers look prime. For 39, Prime tempts because 2 does not divide it. Ask, "Does 3 go into 39?" Thirteen times, so it is composite. Remember too that 2 is the only even prime. Then say, "You hunted for a factor before deciding."