Numbers and Operations Use groups of 4. Materials: Index cards, watches or clocks showing seconds

Tap It Out

Write the numbers 10, 12, 15, and 18 on cards, one number per card. Mix the cards and place them in a row face down.

Each group member takes a card. All four group members tap a pencil lightly on the floor or on a desk. Then, looking at a watch or a clock that shows seconds, group members tap their pencils every 10, 12, 15, or 18 seconds, depending on the card selected. Stop when all four group members tap their pencils at the same time. How many seconds does this take? What is the least common multiple of 10, 12, 15, and 18? Discuss in your group how the LCM results.