Explain how you can easily decompose 30 with an example in a restaurant. You have 30 people. Half of the want coffee. How many then want tea? Compose to the ten from the given number and count on to 30. Make the jumps on the number line visible to the students. How many did you count on? This is the number that you put in your decomposition. Show the number bond chart of 30. Show that in the left column the number always goes up by one, and in the right column that the number always goes down by one. Ask if students can com up with other decompositions of 30. Practice in the same way with decomposing 23. Ask students to complete the number bond chart without context (images or support story(.
Check that students understand number bond charts to 30 by asking the following questions:
- How do you complete a number bond chart?
- What are tips for decomposing numbers bigger than 20? (skip counting and counting on)
- Why is it useful to be able to decompose numbers?