Найдите значение выражения:

а) $\frac{5}{12} : \frac{10}{3} - \frac{5}{6} \cdot \frac{2}{15}$ 1. $\frac{5}{12} : \frac{10}{3} = \frac{5}{12} \cdot \frac{3}{10} = \frac{1}{4} \cdot \frac{1}{2} = \frac{1}{8}$ 2. $\frac{5}{6} \cdot \frac{2}{15} = \frac{1}{3} \cdot \frac{1}{3} = \frac{1}{9}$ 3. $\frac{1}{8} - \frac{1}{9} = \frac{9}{72} - \frac{8}{72} = \frac{1}{72}$ **Ответ: $\frac{1}{72}$** б) $\frac{4}{25} \cdot \frac{5}{16} + \frac{7}{16} \cdot \frac{4}{5}$ 1. $\frac{4}{25} \cdot \frac{5}{16} = \frac{1}{5} \cdot \frac{1}{4} = \frac{1}{20}$ 2. $\frac{7}{16} \cdot \frac{4}{5} = \frac{7}{4} \cdot \frac{1}{5} = \frac{7}{20}$ 3. $\frac{1}{20} + \frac{7}{20} = \frac{8}{20} = \frac{2}{5}$ **Ответ: $\frac{2}{5}$** в) $\frac{9}{8} : \frac{5}{8} : \frac{3}{10}$ 1. $\frac{9}{8} : \frac{5}{8} = \frac{9}{8} \cdot \frac{8}{5} = \frac{9}{5}$ 2. $\frac{9}{5} : \frac{3}{10} = \frac{9}{5} \cdot \frac{10}{3} = 3 \cdot 2 = 6$ **Ответ: 6**