## Basic College Mathematics (10th Edition)

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