\[Страница\ 110.\]
\[\boxed{\mathbf{17.}}\]
\[(7,8 - 1,8)\ :2 = 6\ :2 = 3\ (м) -\]
\[вторая\ часть.\]
\[4,8\ (м) - первая\ часть\ \]
\[(7,8 - 3 = 4,8).\]
\[4,8\ :3 = \frac{48}{30} = \frac{8}{5} = 1,6.\]
\[Ответ:в\ 1,6\ раза.\]
\[\boxed{\mathbf{18.}}\]
\[1а)\ 2\ к\ 1;\ \ \]
\[2а)\ 8\ к\ 1;\ \ \ \ \]
\[3а)\ \frac{12}{2} = 6\ к\ 1;\]
\[1б)\ 2\ к\ 1;\ \ \]
\[2б)\ \frac{8}{7};\ \ \ \]
\[3б)\ \frac{12}{10} = \frac{6}{5}.\]
\[\boxed{\mathbf{19.}}\]
\[\frac{1}{3}\ :\frac{2}{3} = \frac{1 \cdot 3}{3 \cdot 2} = \frac{1}{2}\]
\[Ответ:\frac{1}{2}.\]