---
title: "Addition and subtraction within 20"
description: "Add and subtract within 20 using strategies such as making ten, decomposing a number leading to ten, and using known facts"
canonical: https://lightmysky.com/learn/mathematics/addition-and-subtraction-within-20-mt_m1W6nTQJ2b
source: https://lightmysky.com/learn/mathematics/addition-and-subtraction-within-20-mt_m1W6nTQJ2b.md
retrieved: 2026-10-19
---

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# Addition and subtraction within 20

Add and subtract within 20 using strategies such as making ten, decomposing a number leading to ten, and using known facts

Subject: Mathematics · Area: Addition & Subtraction · Ages 6 to 7
Page: https://lightmysky.com/learn/mathematics/addition-and-subtraction-within-20-mt_m1W6nTQJ2b

## Ready when they can

- Solve 8 + 6 using making ten: 8 + 2 + 4 = 14
- Solve 13 − 4 by decomposing: 13 − 3 − 1 = 9
- Use a known fact (8 + 4 = 12) to derive 12 − 8 = 4

## Lesson: Bridging through ten

You already know your facts up to 10, like 8 + 2 or 6 − 3. Now you can use those same facts to solve bigger problems, all the way up to 20. The trick is to build a bridge through 10.

*(drawing: 8 + 6: hop 2 to land on 10, then hop 4 more to land on 14.)*

**Example.** Mia has 13 stickers and gives 4 to her friend. She takes away 3 first to land on 10, then 1 more to land on 9. So 13 − 4 = 9.

**Example.** A fact family uses the same three numbers in addition and subtraction. For example, 6 + 5 = 11, 5 + 6 = 11, 11 − 6 = 5, and 11 − 5 = 6. Each equation links the same numbers.

**Recap.** Bridge through 10 to add or subtract, or use a fact you already know.

## Practice

18 questions on this page, each with its working shown.

## Needs first

- [Fluent adding and subtracting within 10](https://lightmysky.com/learn/mathematics/fluent-adding-and-subtracting-within-10-mt__we2TDqnJx)

## Opens up

- [Fluent adding and subtracting within 20](https://lightmysky.com/learn/mathematics/fluent-adding-and-subtracting-within-20-mt__t4afSyZRm)
- [Fluent addition and subtraction](https://lightmysky.com/learn/mathematics/fluent-addition-and-subtraction-mt_3e_PQxwC12)
- [Unknown in Addition & Subtraction](https://lightmysky.com/learn/mathematics/unknown-in-addition-and-subtraction-mt_3JgrHY221M)
- [Generalising Patterns](https://lightmysky.com/learn/mathematics/generalising-patterns-mt_fZTn0W_iZR)
- [Adding within 100](https://lightmysky.com/learn/mathematics/adding-within-100-mt_glPPG-kTQY)
- [Guided Multi-Step Problem Solving](https://lightmysky.com/learn/mathematics/guided-multi-step-problem-solving-mt_O_UOTiMvT_)