Adding and subtracting fractions with unlike denominators

You must first find a common denominator.
Change the fractions to the common denominator.
Then you add or subtract the fractions.
Finally, you may need to reduce the fraction.

Example 1:

Add

1/5 + 1/3

The least common denominator is 15.

Both denominators must become 15.

1/5 + 1/3 = 3/3 * 1/5 + 5/5 * 1/3 = 3/15 + 5/15 = 8/15

Example 2:

Subtract
3/8 - 1/3

The least common denominator is 24.

3/3 * 3/8 - 8/8 * 1/3 = 9/24 - 8/24 = 1/24

Both in addition and subtraction, you only add or subtract the numerators. The denominator of the answer is the common denominator.