Adding and Subtracting Fractions with Unlike Denominators
If the denominators are not the same, then you have to use equivalent fractions which do have a common denominator . To do this, you need to find the least common multiple (LCM) of the two denominators.
For example, suppose you want to add:
The LCM of and is . So, we need to find fractions equivalent to and which have in the denominator. Multiply the numerator and denominator of by , and multiply the numerator and denominator of by .
Now we have like denominators, and we can add as described above.