3. 分数の乗除算(解答)
$$ \begin{eqnarray}
\frac{2}{7} \times {3} &=& \frac{2 \times 3}{7}\\
&=& \frac{6}{7}\\
\\
5 \times \frac{2}{3} &=& \frac{5 \times 2}{3} \\
&=& \frac{10}{3} \\
&=& 3\frac{1}{3} (帯分数でも仮分数でも良い)\\
\\
\frac{8}{11} \div{4} &=& \frac{8}{11 \times 4}\\
&=& \frac{2}{11} \\
\\
6 \div \frac{3}{2} &=& \frac{6 \times 2}{3} \\
&=& \frac{2 \times 2}{1} \\
&=& 4\\
\\
\\
\frac{7}{8} \times \frac{2}{14} &=& \frac{7 \times 2}{8 \times 14}\\
&=& \frac{1 \times 2}{8 \times 2}\\
&=&\frac{1 \times 1}{4 \times 2} \\
&=& \frac{1}{8}\\
\\
\frac{5}{12} \times \frac{3}{4} &=& \frac{5 \times 3}{12 \times 4} \\
&=& \frac{5 \times1}{4 \times 4} \\
&=& \frac{5}{16}
\\
\frac{2}{7} \div \frac{10}{21} &=& \frac{2 \times 21}{7 \times 10} \\
&=& \frac{1 \times 21}{7 \times 5}\\
&=& \frac{1 \times 3}{1 \times 5} \\
&=& \frac{3}{5}
\end{eqnarray}
$$