\[ \begin{align*} \dfrac{1}{2} \times \dfrac{3}{4} &= \dfrac{1\times 3}{2\times 4} \\ &= \dfrac{3}{8} \end{align*} \] \[ \begin{align*} \dfrac{2}{3} \times \dfrac{5}{6} &= \dfrac{2\times 5}{3\times 6} \\ &= \dfrac{10}{18} \\ &= \dfrac{5}{9} \end{align*} \] \[ \begin{align*} \dfrac{4}{5} \times \dfrac{3}{7} &= \dfrac{4\times 3}{5\times 7} \\ &= \dfrac{12}{35} \end{align*} \] \[ \begin{align*} 2 \times \dfrac{3}{8} &= \dfrac{2\times 3}{1\times 8} \\ &= \dfrac{6}{8} \\ &= \dfrac{3}{4} \end{align*} \]