Year 3 - Maths
Add and subtract to and from a 3-digit number bridging 100
Representing 3-digit numbers, comparing and positioning on number lines
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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 will use knowledge of place value to represent a 3-digit number in different ways. They will compare and order 3-digit numbers and position on number lines and unmarked number lines.
Lesson Summary
You will learn to add and subtract to and from a 3-digit number bridging 100.
Key Notes
- Addition and subtraction calculations can represent counting on and back over the 100s boundary.
- When you count on in tens, sometimes the 10s digit only changes and sometimes the 100s digit changes.
- When you count back in tens, sometimes the 10s digit only changes and sometimes the 100s digit changes.
Vocabulary To Learn
- Bridging: A mental strategy which uses addition or subtraction to cross a number boundary.
- Partition: Splitting an object or value down into smaller parts.
- 100s boundary: The point at which numbers change into 100s numbers, or from one set of hundreds to another.
Common Mistakes To Avoid
- Pupils may partition numbers incorrectly when adding or subtracting across a 100s boundary.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
Addition and subtraction calculations can represent counting on and back over the 100s boundary. When you count on in tens, sometimes the 10s digit only changes and sometimes the 100s digit changes.
2. Use this key word in a maths sentence and explain it clearly. 'Bridging'
A mental strategy which uses addition or subtraction to cross a number boundary. Use this word when showing your method, then check your final answer is reasonable.
3. Spot and fix this common maths mistake.
Mistake: Pupils may partition numbers incorrectly when adding or subtracting across a 100s boundary. Correction: Encourage pupils to add or subtract to first the 100s number, using number pairs that total 10 or 100.
More Lessons In This Unit
- Comparing and ordering numbers with 1, 2 and 3 digits Study Guide
- Count forwards and backwards in multiples of 2, 20, 5, 50 and 25 Study Guide
- Count forwards and backwards within 3-digits Study Guide
- Estimate the position of 3-digit numbers on unmarked number lines Study Guide
- Ordering sets of 3-digit numbers Study Guide
- Partition 3-digit numbers in different ways Study Guide
- Position 3-digit numbers on number lines Study Guide
- Represent a 3-digit number up to 1,000 in different ways Study Guide
- Solve problems by adding and subtracting to or from 3-digit numbers Study Guide
- Solve problems by counting forwards and backwards in multiples of 2, 20, 5, 50 and 25 Study Guide
- Use known facts to add and subtract multiples of 100 within 1000 Study Guide
- Use known facts to add and subtract to and from multiples of 100 Study Guide
- Use known facts to solve problems involving partitioning numbers Study Guide
- Write a 3-digit multiple of 10 as a multiplication equation Study Guide
Browse all guides in the Year 3 Maths guide library.