Year 3 - Maths
Add 2 and 3-digit numbers by redistributing
Informal and mental strategies for adding and subtracting two 3-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 will add and subtract two 3-digit numbers using partitioning, adjusting, redistribution and bridging.
Lesson Summary
You will learn to add 2 and 3-digit numbers by redistributing.
Key Notes
- If we subtract 1 from one addend, we must add one to the other added for the sum to remain the same
- When we redistribute, the total amount stays the same at all times
- Depending on the addends, we redistribute 1s or 10s
Vocabulary To Learn
- Redistribute: Redistribution is a way of transforming a sum to make it easier to calculate mentally.
- Inverse: The inverse is the opposite or reverse operation. For example, subtraction is the inverse operation of addition.
- Efficient: Being efficient means finding a way to solve a problem quickly whilst also maintaining accuracy.
Common Mistakes To Avoid
- Pupils will sometimes remove or add ones or tens to one addend and forget to amend the other addend so that the calculation has been transformed but doesn't give the same sum as the original.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
If we subtract 1 from one addend, we must add one to the other added for the sum to remain the same. When we redistribute, the total amount stays the same at all times.
2. Use this key word in a maths sentence and explain it clearly. 'Redistribute'
Redistribution is a way of transforming a sum to make it easier to calculate mentally. Use this word when showing your method, then check your final answer is reasonable.
3. Spot and fix this common maths mistake.
Mistake: Pupils will sometimes remove or add ones or tens to one addend and forget to amend the other addend so that the calculation has been transformed but doesn't give the same sum as the original. Correction: Encourage buddy checking of jottings as the children practise so that they can help each other to be reminded.
More Lessons In This Unit
- Add two 3-digit numbers using adjusting strategies Study Guide
- Add two 3-digit numbers using partitioning Study Guide
- Choose the most efficient strategy to add two 3-digit numbers Study Guide
- Choose the most efficient strategy to subtract from a 3-digit number Study Guide
- Subtract 2 or 3-digit numbers using partitioning and bridging a multiple of 10 Study Guide
- Subtract 3-digit multiples of 10 by finding the difference between them Study Guide
- Subtract a pair of 2-digit numbers by finding the difference Study Guide
- Use addition and subtraction to solve problems in different contexts Study Guide
- Use addition and subtraction to solve problems involving bar charts, pictograms and tables Study Guide
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