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20 votes
20 votes
How do you make denominators the same when subtracting fractions?

User Malindu Sandaruwan
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2.6k points

2 Answers

8 votes
8 votes
Let's take an example.

3/4 - 6/7

The denominators here are 4 & 7.

First you find the LCM (lowest common multiple) of both numbers.

Here is an easy way:
4 ---> 4, 8, 12, 16, 20, 24, 28, 32, 36, 40
7 ---> 7, 14, 21, 28, 35, 42, 49, 56, 63, 70

The least common multiple here is 28.

And so, you multiple both 7 and 4 (which are the denominators) with a number to get 28.

7*4= 28
4*7= 28

Make sure you also apply the same multiplication to the numerator.

So in conclusion:
3*7/4*7 & 6*4/7*4

I hope this helps.
User TonyParker
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2.8k points
14 votes
14 votes

Answer: You need to increase the terms of one or both fractions so both fractions have the same dominator

Step-by-step explanation:

A easiest way to do this is to use the "cross-multiplication"

Cross-multiplication: Cross-multiply the two fractions and create two fractions that have a common denominator

You can also search on yt a tutorial step by step

User Zach Kelling
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2.6k points