12). \(\left(6 - 2\frac{4}{5}\right) \cdot \frac{1}{8} - 1\frac{3}{5} : \frac{1}{4}\)

Решение:

1. \(6 - 2\frac{4}{5} = 6 - \frac{14}{5} = \frac{30 - 14}{5} = \frac{16}{5}\)
2. \(\frac{16}{5} \cdot \frac{1}{8} = \frac{16}{40} = \frac{2}{5}\)
3. \(1\frac{3}{5} = \frac{8}{5}\)
4. \(\frac{8}{5} : \frac{1}{4} = \frac{8}{5} \cdot 4 = \frac{32}{5}\)
5. \(\frac{2}{5} - \frac{32}{5} = -\frac{30}{5} = -6\)

Ответ: -6