\[\boxed{\text{5.210.}}\]
\[\textbf{а)}\ 8\ :7 = \frac{8}{7}\ \]
\[\textbf{б)}\ 1\ :10 = \frac{1}{10}\ \]
\[\textbf{в)}\ 17\ :9 = \frac{17}{9}\ \]
\[\textbf{г)}\ 9\ :1 = \frac{9}{1}\ \]
\[\textbf{д)}\ 25\ :5 = \frac{25}{5}\ \]
\[\textbf{е)}\ 99\ :10 = \frac{99}{10}\]