Colorful House of Math logo
Log in

Find the Common Denominator Using the Times Tables

There are several methods for finding the lowest common factor. I will show you one where you search through the times tables, and one that works no matter what numbers you have.

Searching for the Lowest Common Denominator in the Times Tables

When you want to find the lowest common denominator, you can look through the times tables. In the example below, one of the fractions has 8 as its denominator, and the other has 20. Then you have to find a number you can multiply with 8 to make a multiple of 20.

There are no integers that give you 20 when multiplied by 8. As 20 is the largest of the two denominators, you should look at the next multiple of 20, which is 20 2 = 40. Then you can check if there’s an integer that gives you 40 when multiplied by 8. There is! 8 5 = 40. That means you can expand the first fraction by 5 and the other by 2.

Example 1

Find 3 8 7 20.

3 8 7 20 = 3 5 8 5 7 2 20 2 = 15 40 14 40 = 15 14 40 = 1 40

Want to know more?Sign UpIt's free!
White arrow pointing to the LeftPrevious entry
Find the Common Denominator by Expanding or Simplifying
Next entryWhite arrow pointing to the right
How to Find the Common Denominator Using Factorization