Teacher resources icon

Subtraction of fractions with the different (but related) denominators

To subtract fractions with different denominators we must first convert to equivalent fractions with the same denominator. At this level students work with related fractions.

To subtract \(\dfrac{3}{8}\) from \(\dfrac{7}{8}\) we start at \(\dfrac{7}{8}\) and take a step of \(\dfrac{3}{8}\) to get \(\dfrac{4}{8}\).

\begin{align}1\frac{1}{3} - \frac{5}{6} &= \frac{4}{3} - \frac{5}{6} \text{(convert mixed number to improper fraction)} \\&= \frac{8}{6} - \frac{5}{6} \text{(convert to equivalent fractions with same denominator)} \\&= \frac{3}{6} \\&= \frac{1}{2} \text{(simplify)}\end{align}