---
title: "Adding and subtracting tens mentally"
description: "Add and subtract a two-digit number and tens mentally and using concrete/pictorial representations"
canonical: https://lightmysky.com/learn/mathematics/adding-and-subtracting-tens-mentally-mt_I5j1ZWo2cn
source: https://lightmysky.com/learn/mathematics/adding-and-subtracting-tens-mentally-mt_I5j1ZWo2cn.md
retrieved: 2026-10-19
---

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# Adding and subtracting tens mentally

Add and subtract a two-digit number and tens mentally and using concrete/pictorial representations

Subject: Mathematics · Area: Addition & Subtraction · Ages 6 to 7
Page: https://lightmysky.com/learn/mathematics/adding-and-subtracting-tens-mentally-mt_I5j1ZWo2cn

## Ready when they can

- Calculate 45 + 30 = 75 mentally
- Calculate 82 − 40 = 42 mentally
- Explain that only the tens digit changes when adding/subtracting tens

## Lesson: Adding and Subtracting Tens Mentally

Adding or subtracting tens is a fast trick. Only the tens digit moves. The ones digit stays exactly where it is.

*(drawing: Start at 45. Hop three times by ten: 55, 65, 75. That is 45 + 30.)*

**Example.** Now try 82 − 40. Start at 82 and hop back four times by ten: 72, 62, 52, 42. The ones digit stays 2. Only the tens digit changed, from 8 to 4.

**Tip.** Cover the ones digit with your finger. Add or subtract the tens digits only, then uncover the ones digit. It stays the same.

**Recap.** Adding or subtracting tens moves only the tens digit. The ones digit never changes.

## Practice

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

## Needs first

- [10 More or 10 Less](https://lightmysky.com/learn/mathematics/10-more-or-10-less-mt_kw7xmp68rU)
- [The two digits of a two-digit number](https://lightmysky.com/learn/mathematics/the-two-digits-of-a-two-digit-number-mt_THl9GLxwoL)

## Opens up

- [Adding and subtracting two two-digit numbers](https://lightmysky.com/learn/mathematics/adding-and-subtracting-two-two-digit-numbers-mt_UQnAFPs83F)