Common Denominators - Fractions - What is the lowest common denominator?
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Common Denominators

If you want to add two fractions together, both fractions must have the same denominator. That's okay if you want to add 1/9 and 4/9 = 5/9. But what if you need to add 1/9 and 4/7? How can you add them? You need to change one or both of those fractions so that they have the same denominator.

How can you get 1/9 and 4/7 to both have the same denominator? You need to find a number that has both 9 and 7 as factors.

More about factors
More about fractions

Bibliography and further reading about math:

Fractions
Numbers
More Math
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Karen Carr is Associate Professor Emerita, Department of History, Portland State University. She holds a doctorate in Classical Art and Archaeology from the University of Michigan. Follow her on Instagram or Twitter.
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