Your turn — Find the LCM

For each pair, find the lowest common multiple.

Before you build: predict the answer, or work it out mentally if you can.

Then use the rods to model your answer. Build the multiples and show where the two trains first line up. A useful scaffold is to start with a train of six of the smaller-valued rod, then place the larger-valued rod alongside it one at a time. Add more rods if you need them.

Record the multiples you used and write the LCM.

1. 2 and 3
2. 3 and 5
3. 2 and 4
4. 3 and 6
5. 6 and 8
6. 6 and 9

Look again: These six questions were not chosen at random. Can you sort them into three groups? What is similar about the questions in each group?