\[\boxed{\mathbf{2.}\mathbf{357}}\]
\[\textbf{а)}\ \frac{1^{\backslash 7}}{4} + \frac{1^{\backslash 4}}{7} = \frac{7}{28} + \frac{4}{28} = \frac{11}{28}\]
\[\textbf{б)}\ \frac{1^{\backslash 5}}{4} - \frac{1^{\backslash 4}}{5} = \frac{5}{20} - \frac{4}{20} = \frac{1}{20}\]
\[\textbf{в)}\ 3\frac{1^{\backslash 4}}{2} + 2\frac{3}{8} = 3\frac{4}{8} + 2\frac{3}{8} = 5\frac{7}{8}\]
\[\textbf{г)}\ 3\frac{1^{\backslash 5}}{3} - 1\frac{1^{\backslash 3}}{5} = 3\frac{5}{15} - 1\frac{3}{15} =\]
\[= 2\frac{2}{15}\]
\[\textbf{д)}\ 4 - 2\frac{4}{7} = 3\frac{7}{7} - 2\frac{4}{7} = 1\frac{3}{7}\]
\[\textbf{е)}\ 2\frac{3}{4} - 1\frac{5}{6} = 1\frac{7^{\backslash 3}}{4} - 1\frac{5^{\backslash 2}}{6} =\]
\[= 1\frac{21}{12} - 1\frac{10}{12} = \frac{11}{12}\ \]