This activity will give children plenty of practice in figuring out the lowest common multiple of two numbers.
What You Need:
- Index cards
- Permanent marker
What You Do:
- Write numbers on at least 20 index cards, making sure that most of the numbers are not prime. For example, you might choose numbers such as 8 (which has the factors 2 and 4) or 9 (which has 3 as a factor) more often than 7 or 11, which are both prime. Most of the numbers should be between 1 and 20, with a few larger ones that have a lot of factors (e.g., 20, 24, 30).
- Divide the pile of index cards in half into two smaller piles, and give each player one of these smaller piles.
- Both players call out “1, 2, 3…war!” and simultaneously turn over the top card in their piles and place it between them.
- The goal: as quickly as each player can, calculate the lowest common multiple of the numbers on the two cards, and call it out.
- The first player to call out the correct lowest common multiple wins the round and gets to add both of the cards to the bottom of her pile. Repeat Steps 3 and 4 for the next round.
- The game ends when one player runs out of cards. The other player is the winner.
