\[\left( 2\frac{3}{8} - 1\frac{5}{6} \right)\ :\left( - 1\frac{5}{8} \right) =\]
\[= \left( 2\frac{9}{24} - 1\frac{20}{24} \right)\ :\left( - \frac{13}{8} \right) =\]
\[= \left( 1\frac{33}{24} - 1\frac{20}{24} \right) \cdot \left( - \frac{8}{13} \right) =\]
\[= \frac{13}{24} \cdot \left( - \frac{8}{13} \right) = - \frac{1}{3}\]