9. Вычислите: $$\frac{7}{13} + \frac{3.3}{13} \times (\frac{2}{21} - \frac{3}{28}) - \frac{1}{5} = $$

Решение: 1. $$\frac{2}{21} - \frac{3}{28} = \frac{2 \cdot 4}{21 \cdot 4} - \frac{3 \cdot 3}{28 \cdot 3} = \frac{8}{84} - \frac{9}{84} = -\frac{1}{84}$$ 2. $$\frac{3.3}{13} \times (-\frac{1}{84}) = -\frac{3.3}{13 \cdot 84} = -\frac{3.3}{1092}$$ 3. $$\frac{7}{13} - \frac{3.3}{1092} - \frac{1}{5} = \frac{7}{13} - \frac{33}{10920} - \frac{1}{5} = \frac{7 \cdot 840 - 33 - 1 \cdot 2184}{10920} = \frac{5880 - 33 - 2184}{10920} = \frac{3663}{10920} = \frac{1221}{3640}$$ Ответ: $$\frac{1221}{3640}$$