6. Вычислите: \( \frac{7}{10} - \frac{9}{49} : (3-1\frac{13}{14}) + \frac{2}{5} \)

Решение:

1. \( 3-1\frac{13}{14} = 3 - \frac{27}{14} = \frac{42-27}{14} = \frac{15}{14} \)
2. \( \frac{9}{49} : \frac{15}{14} = \frac{9}{49} \cdot \frac{14}{15} = \frac{9 \cdot 14}{49 \cdot 15} = \frac{3 \cdot 2}{7 \cdot 5} = \frac{6}{35} \)
3. \( \frac{7}{10} - \frac{6}{35} = \frac{7 \cdot 7 - 6 \cdot 2}{70} = \frac{49-12}{70} = \frac{37}{70} \)
4. \( \frac{37}{70} + \frac{2}{5} = \frac{37 + 2 \cdot 14}{70} = \frac{37+28}{70} = \frac{65}{70} = \frac{13}{14} \)

Ответ: \(13/14).