How Do You Add Two Fractions With Different Denominators Using Cross Multiplication?
Multiply the numerator of the first fraction by the denominator of the second fraction. For example if you are adding two thirds (2/3) to one fifth (1/5) you would multiply 2 by 5 to get 10. Multiply the numerator of the second fraction by the denominator of the first fraction. In our example we would multiply 1 by 3 to get 3. Add the two new numerators and place their sum as the numerator over the product of the original denominators. This is your answer. In our example the sum of the two new numerators is 10+3 = 13 and the product (multiply) of the two original denominators is 3 x 5 or 15 so the answer is 13/15.
