Year 3 - Maths
Use addition and subtraction to solve problems in different contexts
Informal and mental strategies for adding and subtracting two 3-digit numbers
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Study Guides
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 use addition and subtraction strategies to solve problems in different contexts.
Key Notes
- By looking carefully at the numbers involved, you can choose the most efficient strategy.
- When numbers are close together, finding the difference is the most efficient strategy.
- Sometimes, we can use known addition facts to make finding the difference even more efficient.
Vocabulary To Learn
- Minuend: The minuend is the number being subtracted from.
- Subtrahend: A subtrahend is a number subtracted from another.
- Difference: The difference is the result after subtracting one number from another.
- Partition: Partition is the act of splitting an object or value down into smaller parts.
Common Mistakes To Avoid
- On the magic squares, children will often miss the fact that it is a two step problem involving addition and subtraction. They may think you have to add the two numbers in the row/column or diagonal.
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 numbers involved, you can choose the most efficient strategy. When numbers are close together, finding the difference is the most efficient strategy.
2. Use this key word in a maths sentence and explain it clearly. 'Minuend'
The minuend is the number being subtracted from. Use this word when showing your method, then check your final answer is reasonable.
3. Spot and fix this common maths mistake.
Mistake: On the magic squares, children will often miss the fact that it is a two step problem involving addition and subtraction. They may think you have to add the two numbers in the row/column or diagonal. Correction: Start with a simpler magic square. The easier ones feature the numbers 1-9 and total 15 diagonally, vertically or horizontally. Once they understand them, introduce 2-digit and 3-digit magic squares.
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 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 involving bar charts, pictograms and tables Study Guide
Browse all guides in the Year 3 Maths guide library.