--- title: "Mental and written addition and subtraction" description: "Solve addition and subtraction problems using mental and written methods, including problems involving numbers, quantities, and measures" canonical: https://lightmysky.com/learn/mathematics/mental-and-written-addition-and-subtraction-mt_wzAZ8qFDc4 source: https://lightmysky.com/learn/mathematics/mental-and-written-addition-and-subtraction-mt_wzAZ8qFDc4.md retrieved: 2026-10-19 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Mental and written addition and subtraction Solve addition and subtraction problems using mental and written methods, including problems involving numbers, quantities, and measures Subject: Mathematics · Area: Addition & Subtraction · Ages 6 to 7 Page: https://lightmysky.com/learn/mathematics/mental-and-written-addition-and-subtraction-mt_wzAZ8qFDc4 ## Ready when they can - Solve a two-step problem: 'I had 35p, spent 12p, then found 5p. How much now?' - Choose an appropriate method (mental or written) for a given problem - Solve problems involving measures, e.g. 'a ribbon is 45cm, I cut off 18cm' ## Lesson: Solving money, length and weight problems Real problems do not always look like a plain sum. A price, a ribbon, or a bag of flour can hide an addition or a subtraction inside it. Read the problem carefully: are things going up, going down, or both? *(drawing: Leo had 35p. He spent 12p, then found 5p. Follow the hops: 35 down to 23, then up to 28.)* **Example.** A ribbon is 45cm long. Priya cuts off 18cm to wrap a gift. How long is it now? Subtract, because a piece is taken away: 45cm - 18cm = 27cm. Round, easy numbers like 50 - 20 are quick to do in your head. Numbers with borrowing, like 84 - 37, are safer to write down in columns. Whichever way you pick, check your answer by working backwards. **Recap.** Read the problem to see if things are joining or leaving, then add or subtract, using your head for easy numbers and paper for tricky ones. ## Practice 18 questions on this page, each with its working shown. ## Needs first - [Adding and subtracting two two-digit numbers](https://lightmysky.com/learn/mathematics/adding-and-subtracting-two-two-digit-numbers-mt_UQnAFPs83F) - [Early Word Problems](https://lightmysky.com/learn/mathematics/early-word-problems-mt_VAWV_l7J0D) ## Opens up - [Mentally adding and subtracting ones with 3-digit numbers](https://lightmysky.com/learn/mathematics/mentally-adding-and-subtracting-ones-with-3-digit-numbers-mt_oDU_8zMZjp)