---
title: "Adding within 100"
description: "Add within 100 using strategies based on place value, including adding a two-digit and one-digit number, and a two-digit and a multiple of 10"
canonical: https://lightmysky.com/learn/mathematics/adding-within-100-mt_glPPG-kTQY
source: https://lightmysky.com/learn/mathematics/adding-within-100-mt_glPPG-kTQY.md
retrieved: 2026-10-19
---

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# Adding within 100

Add within 100 using strategies based on place value, including adding a two-digit and one-digit number, and a two-digit and a multiple of 10

Subject: Mathematics · Area: Addition & Subtraction · Ages 6 to 7
Page: https://lightmysky.com/learn/mathematics/adding-within-100-mt_glPPG-kTQY

## Ready when they can

- Calculate 46 + 7 using place value (46 + 4 + 3 = 53)
- Calculate 38 + 40 = 78 using tens understanding
- Relate the strategy to a written method and explain the reasoning

## Lesson: Adding within 100

You already know how to split a two-digit number into tens and ones. You can use that trick to add bigger numbers too. Keep the tens steady and work out the ones first.

**Example.** Try 46 + 7. The 46 has 4 tens and 6 ones. First jump to the next ten: 46 + 4 = 50. That uses up 4 of your 7. There are 3 left, so 50 + 3 = 53. So 46 + 7 = 53.

*(drawing: 38 + 40: jump by tens four times, from 38 to 78. The 8 ones never change.)*

**Tip.** If you write 46 and 7 on top of each other to add them, the 7 goes under the 6, because both are ones. Lining up the columns is the same idea as keeping tens and ones apart in your head.

**Recap.** Split the numbers into tens and ones, add each part, then put them back together.

## Practice

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

## Needs first

- [Addition and subtraction within 20](https://lightmysky.com/learn/mathematics/addition-and-subtraction-within-20-mt_m1W6nTQJ2b)
- [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

- [Fluent adding and subtracting within 100](https://lightmysky.com/learn/mathematics/fluent-adding-and-subtracting-within-100-mt_cChv2j_-Da)
- [Choosing a tool or representation](https://lightmysky.com/learn/mathematics/choosing-a-tool-or-representation-mt_zMEvtigoM3)