Addition to 20 making tens on the number line

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Students learn to add to 20 on the number line, and they learn to make tens to simplify their addition.

The interactive whiteboard shows a number of addition problems, whose answer is always ten. One of the numbers in the problem is hidden by a paint splatter. Students determine which numbers are needed to compose ten.

First, go over how to count the strawberries on the interactive whiteboard. Next, explain how to add using the number line. Start with a number line that is labeled from one to ten, and then move to a blank number line. Explain that students must first look at the first addend, the number before the plus (+) sign. This number is where you start on your number line. The second addend, or the number after the plus (+) sign, is the one that is added to the first number. They can take steps of one to count to the next number. Tell students, however, that it is useful to make ten and then count on with their addition. That means that you must be able to decompose a number. Once you have taken all the steps, you are at the total or answer. To check that students can add on the number line by making tens, ask them to practice with some more addition problems. Emphasize that students can make different steps on the number line, for example going one by one, or by taking bigger steps- but that it is always easiest to make ten first, and then count on.

To check that students can add to twenty making ten on the number line you can ask the following questions:

- Which number do we look at in an addition problem to determine the number we start at on the number line?

- Which number do we look at in an addition problem to determine how far we move on the number line?

- What is a useful first step?

- How do you know what the answer is?

Students first practice addition on the number line with a complete number line from one to ten. Next, they see a blank number line, but the steps are shown, and finally students must determine the steps to take and the total.

Repeat the importance of being able to add to 20 making tens on the number line. The interactive whiteboard shows three different addition problems and three number lines. Students must match the number lines to the addition problems. Ask students how they determined their answer. Remind that they first must look at the first addend to determine where they start on the number line. You can also have the students solve for the total.

If students have difficulty with this goal, it is important that they refresh the number line to 20. Also, they must be comfortable composing 10 from all numbers. You can have students practice by giving them number cards from 1 to 9 and having them compose 10 from the card they draw.

Optional: number cards to 10

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