IGCSEMathsEdexcelMaths AFoundationRevision Notes1. Numbers & the Number SystemFractionsAdding & Subtracting Fractions

Adding & Subtracting Fractions (Edexcel IGCSE Maths A) : Revision Note

Naomi C

Written by: Naomi C

Reviewed by: Dan Finlay

Updated on

Edexcel Maths A: FoundationEdexcel Maths A (Modular): Higher Unit 1Edexcel Maths A: HigherCambridge (CIE) International Maths: ExtendedCambridge (CIE) International Maths: CoreCambridge (CIE) Maths: ExtendedCambridge (CIE) Maths: Core

Did this video help you?

Adding & Subtracting Fractions

How do I add or subtract two fractions?

  • Addition and subtraction are treated in exactly the same way when dealing with fractions

    • Find the lowest common denominator

    • Write each fraction as an equivalent fraction over this denominator

    • Add (or subtract) the numerators and write this over a single denominator

      • Do not add the denominators

    • Simplify the fraction by cancelling common factors

What do I do if any of the fractions are mixed numbers?

  • Convert any mixed numbers into improper fractions

    • Add or subtract the fractions as usual

    • Remember to convert the answer back to a mixed number if required

Examiner Tips and Tricks

In most questions, you can just use your calculator to add or subtract fractions. However, sometimes you get asked to show your working without using a calculator.

Worked Example

(a) Find 2 over 3 plus 1 fifth.

Find the lowest common denominator of 3 and 5
15 is the smallest number that can be divided by both 3 and 5

The lowest common denominator is 15

Write both fractions as equivalent fractions with a common denominator of 15
Multiply the numerator and denominator of the first fraction by 5
Multiply the numerator and denominator of the second fraction by 3

fraction numerator 2 cross times 5 over denominator 3 cross times 5 end fraction plus fraction numerator 1 cross times 3 over denominator 5 cross times 3 end fraction equals 10 over 15 plus 3 over 15 

Add the numerators and write over a single denominator

fraction numerator 10 plus 3 over denominator 15 end fraction equals 13 over 15 

There are no common factors that will cancel

bold 13 over bold 15

(b) Find 3 3 over 4 minus 5 over 8 giving your answer as a mixed number.

Change the mixed number into an improper fraction

Multiply the denominator by the whole part and add to the numerator
Write this value over the denominator

fraction numerator 4 cross times 3 plus 3 over denominator 4 end fraction equals 15 over 4 

Find the lowest common denominator of 4 and 8
8 is the smallest number that by divided by both 4 and 8
The lowest common denominator is 8

Write both fractions as equivalent fractions over 8
Multiply the numerator and denominator of the first fraction by 2

fraction numerator 15 cross times 2 over denominator 4 cross times 2 end fraction minus 5 over 8 equals 30 over 8 minus 5 over 8

Subtract the numerators and write over a single denominator

fraction numerator 30 minus 5 over denominator 8 end fraction equals 25 over 8

Change into a mixed number
Divide 25 by 8 to get 3 remainder 1

bold 3 bold 1 over bold 8

You've read 0 of your 5 free revision notes this week

Sign up now. It’s free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

  • I would just like to say a massive thank you for putting together such a brilliant, easy to use website.I really think using this site helped me secure my top gradesin science and maths. You really did save my exams! Thank you.

    Beth
    IGCSE Student

  • This website is soooo useful and I can’t ever thank you enough for organising questions by topic like this. Furthermore, the name of the website could not have been more appropriate as it literally did SAVE MY EXAMS!

    Fathima
    A Level Student

Did this page help you?

Previous:Mixed Numbers & Improper FractionsNext:Multiplying & Dividing Fractions
Author
Reviewer
Naomi C

Author: Naomi C

Expertise: Maths

Naomi graduated from Durham University in 2007 with a Masters degree in Civil Engineering. She has taught Mathematics in the UK, Malaysia and Switzerland covering GCSE, IGCSE, A-Level and IB. She particularly enjoys applying Mathematics to real life and endeavours to bring creativity to the content she creates.

Dan Finlay

Reviewer: Dan Finlay

Expertise: Maths Lead

Dan graduated from the University of Oxford with a First class degree in mathematics. As well as teaching maths for over 8 years, Dan has marked a range of exams for Edexcel, tutored students and taught A Level Accounting. Dan has a keen interest in statistics and probability and their real-life applications.

Download notes on Adding & Subtracting Fractions