Write down the addition or subtraction sentence. An example of an addition sentence might be:
1/4 + 2/4 = __. An example of a subtraction sentence might be: 5/6 - 1/3 = __.
Look at the numerators and the denominators of each fraction. The numerators are the top numbers (or the numbers to the left of the division bar), and the denominators are the bottom numbers (or the numbers to the right of the division bar).
Add or subtract the numerators if the denominators are the same. In the addition example -- 1/4 + 2/4 -- the denominators are the same. Therefore, you can add 1 and 2 to get the answer 3/4.
Find a common denominator before adding or subtracting if the denominators are not the same. A common denominator is a number into which both denominators in a problem will divide evenly. In the subtraction example 5/6 - 1/3, the denominators aren't the same. Both denominators will divide evenly into the number 6. Rewrite the problem with 6 as the denominator for both fractions in this example.
Adjust the numerators and add or subtract. In this example, you don't have to adjust 5/6 because you only had to multiply 6 times 1 to get the common denominator of 6. If you multiply 1 times the numerator, you have 5, which means that this fraction is left unchanged. In the fraction 1/3, you had to multiply 3 times 2 to get the common denominator. Therefore, you must multiply the numerator times 2 as well, which gives you the fraction 2/6. Then you can subtract 2/6 from 5/6 to get 3/6.
Simplify your answer if possible. If both numbers in the fraction can be divided by a common factor, then you can simplify. In this example, you can divide 3 and 6 by 3 to get the simplified answer 1/2.