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How to subtract fractions with unlike denominators

When the denominators in the fractions you want to subtract from each other are different, things get a little more complicated than subtracting fractions with like denominators.

Let’s say we want to subtract 1/6 from ½.

subtracting unlike fractions

Find the least common multiple

First, we need to find the Least Common Multiple (LCM) for the denominators. Basically, we need to find a common multiple that they share.

The common multiples of 2 are 2, 4, 6, etc.
The common multiples of 6 are 6, 12, 18, etc.

The least common multiple is (3, 1) = 6.

That means in the first fraction we multiply the nominator and denominator by 3 to make the denominator 6 – equal to the denominator in the second fraction.

least common multiple
Subtract the fractions

Now our fractions problem looks like this:

subtracting unlike fractions
Simplify the fraction

Now all we need to do is simplify the fraction. In an earlier blog about adding fractions, we described how to simplify fractions. If you need to review how to simplify fractions, you can read about that here.

simplify the fraction

Worksheets to practice subtracting fractions with different denominators

If you are looking to practice subtracting fractions with unlike denominators, check out our grade 5 fractions worksheets.