Subtracting Fractions with Unlike Denominators

Contributor: Rachel Lewis. Lesson ID: 12778

What is 12/30 - 3/90? That may look complicated, but if you know your common denominators, you can solve this in a fraction of the time! Learn these 3 simple steps and you'll be "cooking" in no time!



learning style
Kinesthetic, Visual
personality style
Grade Level
Intermediate (3-5)
Lesson Type
Quick Query

Lesson Plan - Get It!


We can’t subtract two denominators when they do not have anything in common. So, how do we subtract fractions with unlike denominators, like 928 - 1356?

Fractions tell us how many parts are in a whole.

When fractions have different denominators, they have a different number of parts. When the parts are not the same size, we cannot subtract two fractions.

To subtract fractions with unlike denominators, we can follow three easy steps.

Step One Find a common denominator. Multiply the numerators by the same factor you used to find the common denominator.

Step Two Subtract the numerators. Keep the denominator the same.

Step Three Simplify the fraction, if needed.

Take a moment to put these steps into practice. Look at the example below:

What is 1316?

Step One To find the common denominator, we need to find the least common multiple of the two denominators. The least common multiple between 3 and 6 is 6. We need to multiply the denominator and numerator by the factor that gives us our common denominator. To get the common denominator of 6, we must multiply 3 by 2:

  1 x 2 = 2
  3 x 2 = 6


Step Two Subtract the numerators. Keep the denominators the same:

  2 - 1 = 1
  6 6 = 6


Step Three 16 is in its simplest form. We do not need to simplify the fraction.

So, 1/316 = 16.

Read Subtracting Fractions with Unlike Denominators from Look at the models to visualize subtraction problems. How can you use the models to help you find the difference between two fractions with unlike denominators? Share your response with a parent or teacher.

You have learned how to use pencil and paper to subtract fractions with unlike denominators. You have also used models to visualize subtraction problems.

Now, use your new strategies to complete the practice problems and activities in the Got It? section.

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