Adding & Subtracting Fractions with Unlike Denominators

Today we are going to learn how to add and subtract fractions with unlike denominators. First, we have some definitions to write down.

Fraction- a numerical quantity that is not a whole number. Ex: 1/4, 2/3

Denominator- the number on the bottom of the fraction. Ex: 1/4 the four is the denominator.

Numerator- the number on the top of the fraction. 1/4 the one is the numerator.

Before we can start, you have to know how to add and subtract fractions with unlike denominators.

  • First, you need to find a common denominator.
  • You could multiply the two denominators together or find the least common multiple.
  • When you find the LCM, multiply the denominator by the number to equal the LCM. Ex: 1/4 and 2/3 the LCM is 12, so multiply 4 by 3 and 3 by 4. Then, you have your new denominator
  • Secondly, you need new numerators. Whatever you multiplied the denominator by, you multiply the numerator by. Ex: 1/4 and 2/3 multiply 1 by 3 and 2 by 4
  • Your whole new fractions would be: 3/12 + 8/12= 11/12
  • The next step is to either; add or subtract.
  • The last step, is to simplify.

Now, we are going to do some example problems.

1/5 + 2/3

3/8 + 4/7





Do these on your own.

4/5 + 7/8

2/4 + 5/7

7/9 + 3/4

Now let's try some subtraction.

4/5 - 3/4

5/6  - 4/5

2/3- 1/2





That is how you add and subtract fractions with unlike denominators.

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