Addition within 20

Learning focus

Learn how to add by counting on within 20.

This lesson includes:

  • a catch-up quiz
  • a learning summary


To get started, let's see how well you know this topic already. Take the catch-up quiz below to find out.


Look at the picture below. What can you see? How would you describe it to a friend?

There are 9 butterflies and 11 spiders.

9 + 11 = 20

There are 20 creatures altogether.

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.

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


Test your skills on this topic even further by playing Karate Cats Maths - see if you can collect a new costume for your cat!

Game - Karate Cats Maths

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