---
title: "Inverse: addition undoes subtraction"
description: "Recognise and use the inverse relationship between addition and subtraction to check calculations and solve missing-number problems"
canonical: https://lightmysky.com/learn/mathematics/inverse-addition-undoes-subtraction-mt_ehGS_uVSJv
source: https://lightmysky.com/learn/mathematics/inverse-addition-undoes-subtraction-mt_ehGS_uVSJv.md
retrieved: 2026-10-19
---

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# Inverse: addition undoes subtraction

Recognise and use the inverse relationship between addition and subtraction to check calculations and solve missing-number problems

Subject: Mathematics · Area: Addition & Subtraction · Ages 6 to 7
Page: https://lightmysky.com/learn/mathematics/inverse-addition-undoes-subtraction-mt_ehGS_uVSJv

## Ready when they can

- Check 15 + 7 = 22 by calculating 22 − 7 = 15
- Use the inverse to solve: □ + 9 = 14, so □ = 14 − 9 = 5
- Explain that addition and subtraction 'undo' each other

## Lesson: Addition and subtraction undo each other

Addition and subtraction are opposites. If you add a number and then subtract that same number, you end up back where you started. This is called the inverse, and it lets you check your answers.

*(drawing: Start at 15. Hop +7 to reach 22. Hop back −7 and you land on 15 again.)*

**Example.** Mia works out 15 + 7 = 22. To check her answer, she does the inverse: 22 − 7. She gets 15 again, the number she started with, so she knows her addition was right.

**Tip.** You can use the same trick to find a missing number. If □ + 9 = 14, undo the addition: 14 − 9 = 5. So the missing number is 5.

**Recap.** Addition and subtraction undo each other, so you can use one to check or find the other.

## Practice

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

## Needs first

- [Finding a missing number in addition](https://lightmysky.com/learn/mathematics/finding-a-missing-number-in-addition-mt_ezc2m_0dzN)

## Opens up

- [Unknown in Addition & Subtraction](https://lightmysky.com/learn/mathematics/unknown-in-addition-and-subtraction-mt_3JgrHY221M)
- [Connecting Representations](https://lightmysky.com/learn/mathematics/connecting-representations-mt_EBYGhd8X3x)
- [Estimating by rounding](https://lightmysky.com/learn/mathematics/estimating-by-rounding-mt_QaYfeVL-0C)