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.

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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, Pinterest, or Twitter, or buy her book, Vandals to Visigoths.
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, or buy her book, Vandals to Visigoths.
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