Решение:
а) $\frac{-3}{5} : \frac{5}{-9} = \frac{-3}{5} * \frac{-9}{5} = \frac{-3 * (-9)}{5 * 5} = \frac{27}{25} = 1\frac{2}{25}$;
б) $\frac{16}{-25} : \frac{8}{-15} = \frac{16}{-25} * \frac{-15}{8} = \frac{\overset{2}{\cancel{16}} * \overset{3}{\cancel{(-15)}}}{\underset{5}{\cancel{(-25)}} * \underset{1}{\cancel{8}}} = \frac{2 * 3}{5 * 1} = \frac{6}{5} = 1\frac{1}{5}$;
в) $\frac{9}{-10} : \frac{1}{2} = \frac{9}{-10} * \frac{2}{1} = \frac{9 * \underset{1}{\cancel{2}}}{\underset{-5}{\cancel{(-10)}}} = -\frac{9}{5} = -1\frac{4}{5}$;
г) $\frac{2}{3} : \frac{6}{-7} = \frac{2}{3} * \frac{-7}{6} = \frac{\overset{1}{\cancel{2}} * (-7)}{3 * \underset{3}{\cancel{6}}} = -\frac{7}{9}$.
Ответ:
а) $1\frac{2}{25}$;
б) $1\frac{1}{5}$;
в) $-1\frac{4}{5}$;
г) $-\frac{7}{9}$.