Adding and Subtracting Fractions | Primary Math eBook

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Adding and Subtracting Fractions | Primary Math eBook

Adding and Subtracting Fractions

Adding and Subtracting Fractions with Like Denominators

When adding or subtracting fractions with the same denominators, we look at the numerators and add/subtract them.

Example:

Add 2/9 and 4/9.

2 + 4 = 6, therefore your answer should be:

2/9 + 4/9 = 6/9

Subtract 2/8 from ⅞.

7 - 2 = 5, therefore:

⅞ - 2/8 = ⅝

Adding and Subtracting Fractions with Unlike Denominators

When adding/subtracting fractions with different denominators, you must first change all fractions so that they have the same denominator. Then, you add their changed numerators as was shown above.

Example:

Add 2/8 and ¾.

Multiples of 8: 8, 16, 24, 32, etc.

Multiples of 4: 4, 8, 12, etc.

LCM = 8

8 x 1 = 8

4 x 2 = 8

Now, we multiply the corresponding numerators:

If necessary, we change the answer into a mixed number (if the answer is an improper fraction).

8/8 = 1

Subtract 2/9 from ½.

Multiples of 9: 9, 18, 27, 36, etc.

Multiples of 2: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20

LCM = 18

9 x 2 = 18

2 x 9 = 18

Note: When adding or subtracting mixed numbers, you must first turn all mixed numbers into improper fractions. Then, follow the steps as described above to calculate the answer.