Adding and Subtracting Fractions
When adding and subtracting fractions, the first thing to check is if the denominators are the same.
Part 1) Adding and Subtracting Fractions with Like Denominators
If the denominators are the same, then it's pretty easy: just add or subtract the numerators , and write the result over the same denominator.
Part 2) 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.