Year 3 - Maths
Choose the most efficient strategy to add two 3-digit numbers
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 choose the most efficient strategy to add two 3-digit numbers.
Key Notes
- By looking carefully at the addends, we can choose the most efficient addition strategy.
- Sometimes an adjusting strategy is the most efficient.
- Sometimes a redistributing strategy is the most efficient.
- Sometimes a partitioning and bridging strategy is the most efficient.
Vocabulary To Learn
- Partition: Partitioning is the act of splitting an object or value down into smaller parts.
- Adjust: When you adjust you make a small change to a number. This can make a calculation easier to solve mentally.
- Redistribute / redistribution: Redistribution is where part of one addend is moved to another addend.
- Efficient: Working efficiently means finding a way to solve a problem quickly whilst also maintaining accuracy.
Common Mistakes To Avoid
- Pupils will often know one method, such as partitioning, and stick to it without trying any others. Sometimes, some pupils will be very reluctant to move away from written methods such as columns.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
By looking carefully at the addends, we can choose the most efficient addition strategy. Sometimes an adjusting strategy is the most efficient.
2. Use this key word in a maths sentence and explain it clearly. 'Partition'
Partitioning is the act of splitting an object or value down into smaller parts. 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 often know one method, such as partitioning, and stick to it without trying any others. Sometimes, some pupils will be very reluctant to move away from written methods such as columns. Correction: Reinforce the idea of bravery and courage to try new methods. Remind them that efficiency is partly about speed and they might find that other methods only become quick with practice!
More Lessons In This Unit
- Add 2 and 3-digit numbers by redistributing Study Guide
- 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 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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