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How to Add & Subtract Fractions

Once you know the trick to adding and subtracting fractions with different denominators, you'll have no problem with these problems.


  • Step 1: Add fractions with same denominator Add or subtract the numerators and keep the same denominator if the fractions have the same denominator.
  • TIP: The numerator is the number on the top, and the denominator the number on the bottom of the fraction.
  • Step 2: Find a common denominator Find the lowest common denominator to both fractions if they have different denominators. For example, if you add 1/3 plus 3/8, the least common denominator is 24, since three times eight equals 24.
  • TIP: The lowest common denominator is the smallest common multiple of both denominators.
  • Step 3: Rewrite the fractions Rewrite the fractions, using the lowest common denominator. Multiply the numerator by the same number by which you multiplied the denominator.
  • Step 4: Add or subtract the numerators Add or subtract the numerators and write the sum over the common denominator. The sum of 9/24 and 8/24 is 17/24. The difference is 1/24.
  • Step 5: Reduce the fraction If necessary, reduce the fraction by dividing the numerator and denominator by the highest number you can.
  • FACT: A fraction in which the numerator is larger than the denominator is called an improper fraction.

You Will Need

  • Two fractions
  • A pencil and paper

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