Choose a sample addition problem to solve. For example, suppose you're told to solve 1/7 + 2/7.
Add the numerators, but keep the same denominator in your answer. In the example, you would calculate 1 + 2 = 3. Place the 3 over the same numerator, 7. Your answer is 3/7.
Simplify your answer if needed. In the example, the fraction 3/7 cannot be reduced. If the answer were 2/4, however, you would need to divide both the numerator and denominator by the greatest common factor -- in this case, 2. So 2/4 reduces to 1/2.
Choose a subtraction problem to solve. For example, suppose you have a word problem that says a pizza is cut into eight equal slices. Jenny and Bob's mom and dad ate three pieces between them. The parents gave the siblings five slices, but the children ate only three of them. What fraction of the original pizza remains?
Set up the problem: 5/8 - 3/8. Just like in addition, you will keep the same denominator in your answer. Subtract the numerators to get 2, meaning that 2/8 of the original pizza remains.
Simplify your answer. In the fraction 2/8, the greatest common factor of the numerator and denominator is 2. Divide both numbers by 2 to get your answer: 1/4.