How to do add or subtraction fractions?

A fraction a/b consists of a numerator (the part above the bar, a in this example) and a denominator (the part below the bar, b here). In order to add or subtract fractions, we need to make sure the denominators of all terms are the same, and add or subtract the numerators but keeping the denominators unchanged. 

For example, 2/7 + 1/7 = (2+1)/7 = 3/7. 2/7 - 1/7 = (2-1)/7 = 1/7. This is a simple example because the denominators of all terms are alreday the same. However when they are different, we need to use Least Common Muliple (LCM) to covert the fractions into ones with the same denominators, namely LCM. Then do the addtion or subtraction. Let me explain to you with an example. Solve 1/9 + 5/12. Firstly, find LCM of 9 and 12. 9 = 3 x 3. 12 = 2 x 2 x 3. So LCM(9,12) = 2 x 2 x 3 x 3 = 36. Now we need to covert both fractions into ones with denominators 36. essentially coverting1/9 = ?/36. 1/9 = (1x4)/(9x4) = 4/36. 5/12 = (5x3)/(12x3) = 15/36. So 1/9 + 5/12 = 4/36 + 15/36 = 19/36. Done! 

Answered by Michelle L. Maths tutor

2914 Views

See similar Maths GCSE tutors

Related Maths GCSE answers

All answers ▸

Natasha has two bags of fruit. both bags have the same number of fruit in total. 1/3rd of the fruit in bag 1 are apples and 15% of the fruit in bag 2 are apples. There are 20 apples in bag 1, how many apples are in bag 2?


y is directly proportional to (x-1)^2. When x=5, y=4. Find y when x=7.


If 4x + 3y = 4 and x + 2y = 2 what are the values of x and y ?


1: x = 2, 2: y = x + 5 -> Solve this pair of simultaneous equations.


We're here to help

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