Addition within 20

How can we show this?

We can use a part-whole model to show the two groups and the total of 20.

We can use a bar model to show this calculation.

Or a ten frame. By using a ten frame you can easily see that 20 is made up of two 10s.

You can also see that 11 is one more than 10 and 9 is one fewer, but together they total 20.

What number sentences can you make?

From this picture of two ten frames you can make four different number sentences.

11 + 9 = 20

9 + 11 = 20

20 – 11 = 9

20 – 9 = 11

This means that you can check your answer by using an inverse calculation.

11 + 9 = 20

You can check this by using the calculation:

20 – 9 = 11

Activity