Вычислите: a) $$12 \cdot \frac{5}{7} : \frac{6}{7}$$; б) $$(2\frac{1}{3})^2$$; в) $$\frac{4}{5} + \frac{2}{7} : \frac{5}{10}$$.

a) $$12 \cdot \frac{5}{7} : \frac{6}{7} = 12 \cdot \frac{5}{7} \cdot \frac{7}{6} = \frac{12 \cdot 5 \cdot 7}{7 \cdot 6} = \frac{12 \cdot 5}{6} = 2 \cdot 5 = 10$$.

б) $$(2\frac{1}{3})^2 = (\frac{7}{3})^2 = \frac{7^2}{3^2} = \frac{49}{9} = 5\frac{4}{9}$$.

в) $$\frac{4}{5} + \frac{2}{7} : \frac{5}{10} = \frac{4}{5} + \frac{2}{7} \cdot \frac{10}{5} = \frac{4}{5} + \frac{20}{35} = \frac{4}{5} + \frac{4}{7} = \frac{4 \cdot 7 + 4 \cdot 5}{35} = \frac{28 + 20}{35} = \frac{48}{35} = 1\frac{13}{35}$$.

Ответ: a) 10; б) $$5\frac{4}{9}$$; в) $$1\frac{13}{35}$$.