\[\boxed{\mathbf{1.}}\]
\[5 + \frac{3}{8} = 5\frac{3}{8}\]
\[4\frac{8}{9} + 3 = 7\frac{8}{9}\]
\[\frac{2}{5} + 1\frac{1}{5} = 1\frac{3}{5}\]
\[5\frac{6}{11} - \frac{4}{11} = 5\frac{2}{11}\]
\[7\frac{3}{4} - 5 = 2\frac{3}{4}\]
\[3\frac{2}{7} - \frac{2}{7} = 3\]
\[2\frac{5}{14} + 1\frac{3}{14} = 3\frac{8}{14}\]
\[5\frac{11}{19} - 3\frac{6}{19} = 2\frac{5}{19}\]
\[1 - \frac{3}{10} = \frac{7}{10}\]
\[\boxed{\mathbf{2.}}\]
\[\textbf{а)}\ 2\frac{4}{6} + 1\frac{3}{6} = 3\frac{9}{6} = 4\frac{3}{6}\]
\[\textbf{б)}\ 3 - 1\frac{3}{4} = 2\frac{4}{4} - 1\frac{3}{4} = 1\frac{1}{4}\]
\[\boxed{\mathbf{3.}}\]
\[7\frac{11}{15} - \left( x - 3\frac{4}{15} \right) = 2\frac{8}{15}\]
\[x - 3\frac{4}{15} = 7\frac{11}{15} - 2\frac{8}{15}\]
\[x - 3\frac{4}{15} = 5\frac{3}{15}\]
\[x = 5\frac{3}{15} + 3\frac{4}{15}\]
\[x = 8\frac{7}{15}.\]
\[\boxed{\mathbf{4.}}\]
\[1 - вся\ мука.\]
\[1)\ 1 - \left( \frac{7}{20} + \frac{9}{20} \right) = \frac{20}{20} - \frac{16}{20} =\]
\[= \frac{4}{20}\ (часть) - муки\ пошла\ \]
\[на\ ватрушки.\]
\[2)\ 8\ :4 \cdot 20 = 40\ (кг) - муки\ \]
\[было\ у\ \ повара\ вначале.\]
\[Ответ:40\ кг.\]
\[\boxed{\mathbf{5.}}\]
\[(a - a\ :100 \cdot 40)\ :3 \cdot 2\ (тополей) -\]
\[привезли\ в\ парк\ для\ посадки.\]