Greatest common factor

💡 How it plays and why it helps

Twelve cookies and thirty stickers go into identical party bags with nothing left over; how many bags at most? Greatest common factor asks that kind of question on every card. Two numbers appear, such as 35 and 42, both between 4 and 96, and your child types the largest number that divides both. Ten cards make a round in this Grade 6 game, drawn fresh, so a repeat can turn up. Each answer is checked, and a hint is ready.

Every pair here is built the same way. A shared factor from 2 to 12 is multiplied by two numbers that share nothing more, so the answer is always that first factor. The hint asks for both factor lists, then the biggest number found on both. For 12 and 30, the lists meet at 1, 2, 3 and 6. Six wins.

Stopping early is the classic slip. Seeing that 12 and 30 are both even, a child types 2, which divides both but is not the greatest. Ask, "Is there a bigger number that still fits both?" Going up the lists finds 3, then 6. End with, "You kept looking past the first factor."