3 (+27)10 (31-12)

Решим пример:

$$\begin{aligned}
\left(30\frac{4}{5} + 27\frac{2}{5}\right) \cdot \frac{9}{10} : \left(31\frac{16}{25} - 12\frac{6}{25}\right) = \left(\frac{154}{5} + \frac{137}{5}\right) \cdot \frac{9}{10} : \left(\frac{791}{25} - \frac{306}{25}\right) = \frac{291}{5} \cdot \frac{9}{10} : \frac{485}{25} = \frac{291}{5} \cdot \frac{9}{10} \cdot \frac{25}{485} = \frac{291}{1} \cdot \frac{9}{2} \cdot \frac{5}{485} = \frac{291 \cdot 9 \cdot 5}{2 \cdot 485} = \frac{13095}{970} = \frac{2619}{194} = 13\frac{97}{194}
\end{aligned}$$

Ответ:$$13\frac{97}{194}$$