## Introductory Algebra for College Students (7th Edition)

When adding $\frac{1}{5}$ and $\frac{3}{4}$, there are many common denominators that we can use, such as 20, 40, 60, and so on. The given denominators, 4 and 5, divide into all of these numbers. However, the denominator 20 is the smallest number that 4 and 5 divide into. For this reason, 20 is called the least common denominator.