In adding and subtracting fractions with unlike denominators, you have to get a least common denominator which is exactly like the least common multiple it just so happens to be in the denominator.

When adding or subtracting fractions, you need to look at the denominator. If the denominator is the same, then you can just add or subtract the numerator. If the denominator is different ...

She gave the example of the “butterfly” method of adding and subtracting fractions, which relies a multiplication trick to find a common denominator. Jordan said her intervention demonstrates ...