Year 2 - Maths
Add 2-digit numbers when 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 add two-digit numbers when the sum crosses the tens boundary.
Key Notes
- When adding two-digit numbers that cross the tens boundary, both addends can be partitioned, then recombined.
- When adding two-digit numbers that cross the tens boundary, one addend can be partitioned. This is more efficient.
- A number line can be used to find a missing addend when the tens boundary is crossed.
Vocabulary To Learn
- Partition: To split a whole up into parts; a piece or section of a whole.
Common Mistakes To Avoid
- If children partition both addends when addition involves bridging 10, they may forget to add the extra 10 made when combining the ones.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
When adding two-digit numbers that cross the tens boundary, both addends can be partitioned, then recombined. When adding two-digit numbers that cross the tens boundary, one addend can be partitioned. This is more efficient.
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: If children partition both addends when addition involves bridging 10, they may forget to add the extra 10 made when combining the ones. Correction: Encourage children to consider whether an addition will bridge 10 before solving and if so, partition only one addend to reduce the number of steps required, increasing efficiency.
More Lessons In This Unit
- 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
- Subtract two-digit numbers crossing the tens boundary Study Guide
- Use efficient addition strategies to calculate Study Guide
- Use efficient methods to solve subtraction equations Study Guide
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