STRATEGIES TO TEACH COMPOSING AND DECOMPOSING NUMBERS

In this blog post, I will explain what is composing and decomposing numbers.

Decomposing a Number

To decompose a number, you take the whole number and break it down into smaller parts. To decompose the number six, you can break it into smaller parts like 5 and 1 or 3 and 3.

One math strategy you can use to show decomposition is a number bond. A number bond has a big circle and two smaller circles. You put objects in the big circle and move some objects into one circle, called a part, and some into another circle also called a part. Using a number bond, you can decompose a number in many ways. It’s also visual, so students can see how a number can break into smaller parts.

There are many activities you can use to show decomposition. You can play build it and break it, shake and spill, or you can simply give students a number, and they can use a number bond to decompose it.

Here’s a link to a free decomposing numbers worksheet.

Composing a Number

To compose a number, you take smaller numbers and combine them to make a larger number.

An example is 4 and 5 makes 9. If using a number bond, you would put 4 objects in one part, and 5 objects in the other. Then you would move them to the whole so show that the two parts make 9.

Get more composing and decomposing activities here.

Writing Number Sentences

You can show decomposing and composing numbers using words and number sentences. For example, here are some ways to show that 4 and 5 make 9.

4+5=9

5+4=9

9=4+5

9=5+4

Students are usually familiar with writing number sentences by writing the two parts first and then the sum, versus starting with the whole amount and then writing the two parts. It’s important to expose them to both ways of writing.

Want More Composing and Decomposing Activities?

There are many ways to teach students how to compose and decompose numbers that are fun and engaging. I have 20+ low-prep activities that you can use during small groups or math centers.