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Fractions – Adding & Subtracting


Getting to grips with the 4 basic arithmetic operations (Add / Subtract / Multiply / Divide ) when using fractions can easily be achieved once you know some basics rules:

With adding and subtracting, the rule is to make sure the denominators are the same before you can add or subtract fractions. if not, then multiply one (Case II) (or both fractions (Case III) ) by a number so as to end up with fractions having the same number as the denominator.

  • Case I: Fractions have the same denominator. We simply add or subtract the numerator.
  • Case II: Fractions have different denomintors. However, multiplying on of the fractions by a number (in this example by 2) we end up with both fractions having the same denominator.
  • Case III: This is the most complex example. In this case, we have to multiply both fractions by a number so as to obtain the same denominator in both fractions. The first fration is multiplied by 4 an d the second fraction by 7.
The full video lesson on adding and subtracting fractions is found here.