\[2\frac{5}{6} + \left( - 3\frac{7}{8} \right) - \left( - 2\frac{1}{12} \right) - 1\frac{2}{3} =\]
\[= 2\frac{20}{24} - 3\frac{21}{24} + 2\frac{2}{24} - 1\frac{16}{24} =\]
\[= \left( 2\frac{20}{24} + 2\frac{2}{24} \right) - \left( 3\frac{21}{24} + 1\frac{16}{24} \right) =\]
\[= 4\frac{22}{24} - 4\frac{37}{24} =\]
\[= - \left( 4\frac{37}{24} - 4\frac{22}{24} \right) =\]
\[= - \frac{15}{24} = - \frac{5}{8}\]