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.

JB
Answered by Jenny B. Maths tutor

4233 Views

See similar Maths GCSE tutors

Related Maths GCSE answers

All answers ▸

factorise x^2 - 8x -65


Sam works for £14 per hour. When Sam works more than 8 hours a day, he is paid overtime for each hour he works more than 8 hours at 1½ times his normal rate of pay. Sam worked for 12 hours. Work out the total amount of money Sam earned.


How do I solve a quadratic equation?


Solve algebraically: 1) 6a + b = 16, 2) 5a - 2b = 19


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