\[\boxed{\text{5.318.}}\]
\[\textbf{а)}\ \frac{1}{2} = \frac{3}{6} = \frac{12}{24}\]
\[\frac{1}{2} = \frac{1 \cdot 3}{2 \cdot 3} = \frac{3}{6};\ \ \ \ \ \frac{1}{2} = \frac{1 \cdot 12}{2 \cdot 12} = \frac{12}{24}.\]
\[\textbf{б)}\ \frac{4}{6} = \frac{12}{18} = \frac{20}{30}\ \]
\[\frac{4}{6} = \frac{4 \cdot 3}{6 \cdot 3} = \frac{12}{18};\ \ \ \ \frac{4}{6} = \frac{4 \cdot 5}{6 \cdot 5} = \frac{20}{30}\text{.\ }\]
\[\textbf{в)}\ \frac{3}{5} = \frac{15}{25} = \frac{27}{45}\ \]
\[\frac{3}{5} = \frac{3 \cdot 5}{5 \cdot 5} = \frac{15}{25};\ \ \ \ \ \frac{3}{5} = \frac{3 \cdot 9}{5 \cdot 9} = \frac{27}{45}.\]
\[\textbf{г)}\ \frac{12}{14} = \frac{6}{7} = \frac{60}{70}\ \]
\[\frac{6}{7} = \frac{6 \cdot 2}{7 \cdot 2} = \frac{12}{14};\ \ \ \ \frac{12}{14} = \frac{12 \cdot 5}{14 \cdot 5} =\]
\[= \frac{60}{70}\text{.\ \ }\]