\[\boxed{\mathbf{2.}\mathbf{170}}\]
Пояснение.
Решение.
\[\textbf{а)}\ 0,2 + \frac{1}{7} = \frac{2}{10} + \frac{1}{7} =\]
\[= \frac{1^{\backslash 7}}{5} + \frac{1^{\backslash 5}}{7} = \frac{7}{35} + \frac{5}{35} = \frac{12}{35}\]
\[\textbf{б)}\ \frac{5}{6} - 0,25 = \frac{5}{6} - \frac{25}{100} =\]
\[= \frac{5^{\backslash 2}}{6} - \frac{1^{\backslash 3}}{4} = \frac{10}{12} - \frac{3}{12} = \frac{7}{12}\]
\[\textbf{в)}\ \frac{23}{25} + 0,4 = \frac{23}{25} + \frac{4}{10} =\]
\[= \frac{23}{25} + \frac{2^{\backslash 5}}{5} = \frac{23}{25} + \frac{10}{25} = \frac{33}{25} =\]
\[= 1\frac{8}{25}\]
\[\textbf{г)}\ 0,75 - \frac{7}{42} = \frac{75}{100} - \frac{7}{42} =\]
\[= \frac{3^{\backslash 21}}{4} - \frac{7^{\backslash 2}}{42} = \frac{63}{84} - \frac{14}{84} = \frac{49}{84} =\]
\[= \frac{7}{12}\]