13. Вычислите: $$2\frac{4}{13} \cdot (\frac{4}{5} - \frac{7}{12}) - 7 : 3\frac{1}{2}$$

Решение: 1. $$2\frac{4}{13} = \frac{2 \cdot 13 + 4}{13} = \frac{26 + 4}{13} = \frac{30}{13}$$ 2. $$\frac{4}{5} - \frac{7}{12} = \frac{4 \cdot 12 - 7 \cdot 5}{5 \cdot 12} = \frac{48 - 35}{60} = \frac{13}{60}$$ 3. $$\frac{30}{13} \cdot \frac{13}{60} = \frac{30 \cdot 13}{13 \cdot 60} = \frac{30}{60} = \frac{1}{2}$$ 4. $$3\frac{1}{2} = \frac{3 \cdot 2 + 1}{2} = \frac{6 + 1}{2} = \frac{7}{2}$$ 5. $$7 : \frac{7}{2} = 7 \cdot \frac{2}{7} = \frac{7 \cdot 2}{7} = 2$$ 6. $$\frac{1}{2} - 2 = \frac{1}{2} - \frac{4}{2} = \frac{1 - 4}{2} = -\frac{3}{2} = -1\frac{1}{2}$$ **Ответ: -1$$\frac{1}{2}$$**