## Basic College Mathematics (9th Edition)

To rewrite unlike fractions as like fractions, we must find the least common denominator (or the denominator that is the least common multiple of the original denominators) of the unlike fractions. For example, if we want to add $\frac{3}{8}$ and $\frac{1}{4}$, we must find the least common multiple of 4 and 8. We know that this is 8. Therefore, we can rewrite this pair as like fractions. $\frac{3}{8}+\frac{1}{4}=\frac{3}{8}+\frac{1\times2}{4\times2}=\frac{3}{8}+\frac{2}{8}=\frac{3+2}{8}=\frac{5}{8}$