a) $$\frac{9}{56} - (\frac{7}{15} - \frac{5}{12}) \cdot (\frac{3}{14} + \frac{1}{2})$$ б) $$(\frac{2}{3} + \frac{7}{8} - \frac{5}{6}) \cdot (1 - \frac{5}{17})$$ в) $$(3\frac{1}{14} - 2\frac{5}{21}) \cdot (2,7 - 2,1)$$ г) $$(4\frac{13}{18} - 3\frac{7}{9}) \cdot (\frac{1}{2} - \frac{4}{17})$$

Решение:

1. \(\frac{7}{15} - \frac{5}{12} = \frac{28 - 25}{60} = \frac{3}{60} = \frac{1}{20}\)
2. \(\frac{3}{14} + \frac{1}{2} = \frac{3 + 7}{14} = \frac{10}{14} = \frac{5}{7}\)
3. \(\frac{9}{56} - \frac{1}{20} \cdot \frac{5}{7} = \frac{9}{56} - \frac{1}{28} = \frac{9 - 2}{56} = \frac{7}{56} = \frac{1}{8}\)
4. \(3\frac{1}{14} - 2\frac{5}{21} = \frac{43}{14} - \frac{47}{21} = \frac{129 - 94}{42} = \frac{35}{42} = \frac{5}{6}\)
5. \(2,7 - 2,1 = 0,6 = \frac{3}{5}\)
6. \(\frac{5}{6} \cdot \frac{3}{5} = \frac{1}{2}\)
7. \(\frac{2}{3} + \frac{7}{8} - \frac{5}{6} = \frac{16 + 21 - 20}{24} = \frac{17}{24}\)
8. \(1 - \frac{5}{17} = \frac{12}{17}\)
9. \(\frac{17}{24} \cdot \frac{12}{17} = \frac{1}{2}\)
10. \(4\frac{13}{18} - 3\frac{7}{9} = \frac{85}{18} - \frac{34}{9} = \frac{85 - 68}{18} = \frac{17}{18}\)
11. \(\frac{1}{2} - \frac{4}{17} = \frac{17 - 8}{34} = \frac{9}{34}\)
12. \(\frac{17}{18} \cdot \frac{9}{34} = \frac{1}{2} \cdot \frac{1}{2} = \frac{1}{4}\)

Ответ: а) \(\frac{1}{8}\); б) \(\frac{1}{2}\); в) \(\frac{1}{2}\); г) \(\frac{1}{4}\).