\[\frac{7}{8}-\frac{5}{6}=\frac{21}{24}-\frac{20}{24}=\frac{1}{24}.\]
\[\frac{1}{24}\cdot\frac{4}{5}=\frac{4}{120}=\frac{1}{30}.\]
Ответ: \(\frac{1}{30}\).