a) \( \dfrac{5}{8}-\dfrac{2}{5}=\dfrac{25}{40}-\dfrac{16}{40}=\dfrac{9}{40}\)
b) \(1\dfrac{1}{{10}} - \dfrac{3}{4} = \dfrac{{11}}{{10}} - \dfrac{3}{4}\)\( = \dfrac{{22}}{{20}} - \dfrac{{15}}{{20}} = \dfrac{7}{{20}}\)
c) \(\dfrac{2}{3} + \dfrac{1}{2} - \dfrac{5}{6} = \dfrac{4}{6} + \dfrac{3}{6} - \dfrac{5}{6}\)\( = \dfrac{{4 + 3 - 5}}{6} = \dfrac{2}{6} = \dfrac{1}{3} \)