Year 2 - Maths
Subtract two-digit numbers crossing the tens boundary
Addition and subtraction of two 2-digit numbers
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This pupil-friendly study guide includes a unit summary, clear notes, common mistakes, and quick questions with answers.
Unit Summary
In this unit pupils apply their knowledge of known facts and understanding of place value to add and subtract with 2-digit numbers both within and across the tens boundary.
Lesson Summary
You will learn to subtract two-digit numbers crossing the tens boundary.
Key Notes
- When subtracting, the known part of the whole can be partitioned further to subtract the tens and the ones separately.
- Partitioning both the whole and the parts when subtracting gives a correct answer when the ones digits bridge 10
- The tens and ones can be subtracted in any order and the remaining part will stay the same.
Vocabulary To Learn
- Partition: To split a whole up into parts; a piece or section of a whole.
- Part: A piece or section of a whole.
Common Mistakes To Avoid
- Children may spot a pattern and be able to continue it based on noticing numbers simply increasing or decreasing without making the generalisations needed to understand why this happens.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
When subtracting, the known part of the whole can be partitioned further to subtract the tens and the ones separately. Partitioning both the whole and the parts when subtracting gives a correct answer when the ones digits bridge 10.
2. Use this key word in a maths sentence and explain it clearly. 'Partition'
To split a whole up into parts; a piece or section of a whole. Use this word when showing your method, then check your final answer is reasonable.
3. Spot and fix this common maths mistake.
Mistake: Children may spot a pattern and be able to continue it based on noticing numbers simply increasing or decreasing without making the generalisations needed to understand why this happens. Correction: Encourage children to articulate not only the pattern, but also why it has occurred, at first using practical equipment to prove it, then mentally visualising and manipulating the numbers involved.
More Lessons In This Unit
- Add 2-digit numbers when crossing the tens boundary Study Guide
- Add two-digit numbers without crossing the tens boundary Study Guide
- Combine tens and ones within equations Study Guide
- Create addition and subtraction problems Study Guide
- Explain different strategies used to subtract Study Guide
- Find the missing addend when adding two-digit numbers Study Guide
- Find the missing part when subtracting two-digit numbers Study Guide
- Solve equations involving the subtraction of two-digit numbers Study Guide
- Solve problems involving addition and subtraction Study Guide
- Solve problems involving subtraction of two-digit numbers Study Guide
- Solve problems involving subtraction when bridging 10 Study Guide
- Solve problems involving the addition of two-digit numbers Study Guide
- Use efficient addition strategies to calculate Study Guide
- Use efficient methods to solve subtraction equations Study Guide
Browse all guides in the Year 2 Maths guide library.