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.

To add improper fractions: The simplest approach is to add the improper fractions using a common denominator. close common denominatorA denominator that is the same for two or more fractions ...

Fractions, often perceived as daunting, become manageable with the right approach. Addition and subtraction require finding a common denominator, while multiplication involves directly multiplying ...

The common denominator model, while not really a picture, demonstrates that the same rules apply to multiplication and division with fractions. It also shows why “invert and multiply” works.

In addition to emphasizing fractions as points on the number line, the common standards differ from previous standards in other important ways: They delay arithmetic with fractions until students ...