How do I add two fractions? (plus example)

Adding (and subtracting) fractions is more difficult than multiplying them because we need to make sure that the denominators (bottom numbers) are equal in both fractions.

To do this, we may need to change the way we have written the fractions (without actually changing the fractions themselves).

Given the problem

(a/b) + (c/d),

we need to ensure that the denominators are equal.

To do this:

- multiply the top and bottom of the left hand side fraction by b

- multiply the top and bottom of the right hand side fraction by d

(Because we multiply the top AND bottom of the fraction, we essentially still have the same fraction, just written in a different way.)

We now have 

(ad/bd) + (cb/bd).

The denominators are now equal, so we can simply rewrite this as

(ad+cb)/bd, which is our final answer.

 

 

Example: Find (3/4) + (2/5).

We need to 

- multiply top and bottom of left fraction by 5

- multiply top and bottom of right fraction by 4

This gives

((3 x 5) / (4 x 5) )    +    ((2 x 4) / (4 x 5))

which is equal to 

(15/20) + (8/20).

We can now add the fractions (only add the top numbers together!) to get the answer,

23/20.

Answered by Jenny B. Maths tutor

4149 Views

See similar Maths GCSE tutors

Related Maths GCSE answers

All answers ▸

Solve the following simultaneous equation: 1) 2x=y-5, 2) 2y^2=4x^2+4x-15


Given that your grade for your computing is based on 5 coursework that weigh differently, and you know the results of 4: 80, 75, 50 and 90 which weighs 10%, 20%, 45% and 5%. What grade do you need in your last coursework to achieve at least a B (70%)?


f:x-->2x^2+1 and g:x--> 2x/(x-1) where x is not equal to 1. express the composite function gf as simply as possible


How to do Indices?


We're here to help

contact us iconContact usWhatsapp logoMessage us on Whatsapptelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

© MyTutorWeb Ltd 2013–2025

Terms & Conditions|Privacy Policy
Cookie Preferences