2. 解答
$$ \begin{eqnarray}
\frac{1}{5} + \frac{3}{5} &=& \frac{4}{5} \\
\frac{3}{7} -\frac{2}{7} &=& \frac{1}{7} \\
\frac{3}{8} + \frac{1}{8} &=& \frac{2}{8} = \frac{1}{4} \color{red}{(約分できるときは約分しましょう)}\\
\frac{1}{6} + \frac{3}{4} &=& \frac{2}{12} +\frac{9}{12}\\
&=& \frac{11}{12}\\
\\
\frac{2}{5} – \frac{1}{10} &=& \frac{4}{10} -\frac{1}{10} \\
&=& \frac{3}{10}\\
\\
\frac{1}{2} +\frac{1}{3} – \frac{1}{6} &=& \frac{3}{6} + \frac{2}{6} -\frac{1}{6} \\
&=& \frac{3+2-1}{6} \\
&=& \frac{4}{6} \\
&=& \frac{2}{3}
\end{eqnarray}$$