--- title: "Number bonds" description: "Recall number bonds (addition and related subtraction facts) within 20" canonical: https://lightmysky.com/learn/mathematics/number-bonds-mt_s2mfRBoTal source: https://lightmysky.com/learn/mathematics/number-bonds-mt_s2mfRBoTal.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`. # Number bonds Recall number bonds (addition and related subtraction facts) within 20 Subject: Mathematics · Area: Addition & Subtraction · Ages 5 to 6 Page: https://lightmysky.com/learn/mathematics/number-bonds-mt_s2mfRBoTal ## Ready when they can - Quickly recall that 8 + 5 = 13 - Given 13 – 5, respond 8 using knowledge of related addition fact - Know all pairs of single-digit numbers that sum to numbers up to 20 ## Lesson: Number bonds within 20 You already know many number bonds. Every bond makes two facts. One is adding. One is subtracting. If 8 + 5 = 13, then 13 − 5 = 8. *(drawing: 8 stars and 5 stars make 13 stars. Take away 5, and 8 stars are left.)* **Example.** Ravi knows 8 + 5 = 13. His teacher asks 13 − 5. Ravi does not count. He just remembers the bond and says 8. **Tip.** Stuck on a subtraction fact? Turn it into addition. Ask what number, plus the one you took away, makes the whole. **Recap.** Know the addition fact, and its subtraction fact comes free. ## Practice 18 questions on this page, each with its working shown. ## Needs first - [Number bonds to 10](https://lightmysky.com/learn/mathematics/number-bonds-to-10-mt_e8CZ7E5qW7) - [Fluent adding and subtracting within 5](https://lightmysky.com/learn/mathematics/fluent-adding-and-subtracting-within-5-mt_ghF3Vv6taM) ## Opens up - [Place value understanding and number facts](https://lightmysky.com/learn/mathematics/place-value-understanding-and-number-facts-mt_kJGCjnuelW) - [Adding and subtracting](https://lightmysky.com/learn/mathematics/adding-and-subtracting-mt_mr_Vk7FGzK)