Year 3 - Maths
Explain that addition and subtraction of fractions are inverse operations
Composition of non-unit fractions: addition and subtraction
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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 use repeated addition of a unit fraction to form a non-unit fraction. They will compare non-unit fractions with the same denominator. They will add and subtract fractions with the same denominator.
Lesson Summary
You will learn to explain that addition and subtraction of fractions are inverse operations.
Key Notes
- You know that if 3 + 4 = 7 then 7 - 4 = 3
- Facts about whole numbers can be applied to the numerators of fractions with the same denominator.
- If 3 tenths plus 4 tenths is equal to 7 tenths then 7 tenths subtract 4 tenths is equal to 3 tenths.
Vocabulary To Learn
- Additive: Additive equations involve addition or subtraction.
- Inverse: Inverse means the opposite in effect or reverse of. For example, subtraction is the inverse operation of addition.
- Numerator: A numerator is the top number in a fraction. It shows how many parts we have.
- Denominator: A denominator is the bottom number in a fraction. It shows how many parts a whole has been divided into.
Common Mistakes To Avoid
- Children might add or subtract the denominator as well.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
You know that if 3 + 4 = 7 then 7 - 4 = 3. Facts about whole numbers can be applied to the numerators of fractions with the same denominator.
2. Use this key word in a maths sentence and explain it clearly. 'Additive'
Additive equations involve addition or subtraction. Use this word when showing your method, then check your final answer is reasonable.
3. Spot and fix this common maths mistake.
Mistake: Children might add or subtract the denominator as well. Correction: Reinforce to children that the denominator denotes the unit fraction being used in calculation so does not need changing. Count aloud with physical objects to start with before moving onto counting in unit fractions.
More Lessons In This Unit
- Add and subtract fractions with the same denominator in a range of contexts Study Guide
- Add fractions with the same denominator Study Guide
- Add fractions with the same denominator and generalise the rule Study Guide
- Add on fractions with the same denominator Study Guide
- Substitute a fraction representing a whole to solve subtraction problems Study Guide
- Subtract fractions from a whole by converting the whole to a fraction Study Guide
- Subtract fractions with the same denominator Study Guide
- Use repeated addition of a unit fraction to form 1 Study Guide
- Use repeated addition of a unit fraction to form a non-unit fraction Study Guide
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