--- title: "Length word problems within 100" description: "Solve word problems involving lengths within 100, using addition and subtraction with drawings and equations" canonical: https://lightmysky.com/learn/mathematics/length-word-problems-within-100-mt_DLcEzmmj2r source: https://lightmysky.com/learn/mathematics/length-word-problems-within-100-mt_DLcEzmmj2r.md retrieved: 2026-11-12 --- > **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`. # Length word problems within 100 Solve word problems involving lengths within 100, using addition and subtraction with drawings and equations Subject: Mathematics · Area: Measurement · Ages 7 to 8 Page: https://lightmysky.com/learn/mathematics/length-word-problems-within-100-mt_DLcEzmmj2r ## Ready when they can - Solve addition and subtraction word problems about lengths within 100, including missing parts and two changes - Interpret a supplied number-line model or hop description for a length word problem - Choose or check an equation with a symbol for the unknown that represents a length word problem ## Lesson: Solving length word problems Use the same unit for every length; cm means centimetres. Join pieces end to end without overlap: add their lengths. Cut a piece off: subtract its length to find what is left. For two-digit calculations, split the added or removed length into tens and ones. Work with the tens, then the ones. To compare lengths, subtract the shorter length from the longer one. *(drawing: A 45 cm rope loses 18 cm. Split 18 into 10 and 8: 45 - 10 = 35, then 35 - 8 = 27. There are 27 cm left.)* **Example.** Mia places a 62 cm ribbon and a 15 cm ribbon end to end without overlap. Add: 62 + 15 = 77. The total length is 77 cm. Subtracting would find the difference between the two lengths, not their total. For a number-line drawing, mark the starting length. Hop right to add a piece or left to remove one. Label the hop with the piece's length. The landing point shows the new length. To find a missing hop, subtract the smaller endpoint from the larger one. A hop from 54 to 38 removes 54 - 38 = 16 cm. A letter, such as n or p, or the symbol ? can stand for a missing length in centimetres. For a cut, write start - piece = left. A rope starts at 80 cm and has 55 cm left: 80 - n = 55. Find the removed piece by subtracting: 80 - 55 = 25, so n = 25. To find a missing added piece, subtract the start from the total. A strip grows from 26 cm to 44 cm. The added piece is 44 - 26 = 18 cm long. To find the start before a cut, add the cut piece to what is left. If 32 cm remains after a 14 cm cut, the start was 32 + 14 = 46 cm. **Example.** For two changes, work in story order. A 20 cm strip gains 13 cm, then loses 7 cm: 20 + 13 = 33, then 33 - 7 = 26. For two cuts, subtract the first cut, then subtract the second cut from what is left. Write the unit with your answer. Both sides of an equals sign have the same value. You can write n = 50 - 12 or 50 - 12 = n. To find a missing second cut, find the length after the first cut. From 80 cm, cut 20 cm to leave 60 cm. If 37 cm remains after another cut, that cut was 60 - 37 = 23 cm. **Recap.** Use the story to choose addition or subtraction. Show the lengths with an equation or number line, solve, and write the unit. *Lesson, questions and flashcards written for this dataset.* ## Practice 17 questions on this page, each with its working shown. ## Needs first - [Comparing lengths by measuring](https://lightmysky.com/learn/mathematics/comparing-lengths-by-measuring-mt_xWg0lI_gG4) ## Optional connections - [Fluent adding and subtracting within 100](https://lightmysky.com/learn/mathematics/fluent-adding-and-subtracting-within-100-mt_cChv2j_-Da) ## Opens up - [Solving money measurement and time problems](https://lightmysky.com/learn/mathematics/solving-money-measurement-and-time-problems-mt_iQYPw8bMfN)