Composing to 20
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Students learn to compose numbers to 20. They learn to compose by counting on and by adding a few at a time.
It is useful to be able to compose so you know how many of something you need. If you want to share 15 ice cream cones, but only have 13, you know that you need 2 more to get to 15.
Students practice counting amounts to 20 by counting objects- have students write their answers.
Explain composing numbers by using colored pencils. Take 12 pencils and say that you want to have 16. How many more do you need? If you count on from 12 you can compose easily. There will also be students who see with one glance that 4 pencils are needed. Discuss the ret of the examples in this way. Ask students to practice with their own colored pencils. Check that students are ablet to compose numbers by dragging objects to compose to a given number. Ask students to name how many they have added to compose the number.
To check that students understand composing numbers to 20, you can ask the following questions:
- What does it mean to compose a number?
- Are there other things in class that we can compose?
- When is it useful to be able to compose numbers?
Students practice composing numbers to 20 by indicating how many more are needed to compose the given number.
Organize students into pairs. Give each pair 20 blocks and ask them to practice composing to 20 in turns. The first student sets a random number of blocks on the table and the second composes 20. You can vary with composing different numbers. Check that students understood by composing the pencil boxes to 20. Discuss why it is useful to be able to compose numbers and ask if they can come up with any other situations in which it is useful to compose numbers.
Students who have difficulty composing can be supported by practicing with objects in the classroom, like colored pencils or blocks.
colored pencils, blocks
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