19. Вычислите: \(2-\frac{15}{28}:\frac{10}{21}\).

\(2-\frac{15}{28}:\frac{10}{21}=2-\frac{15}{28}\cdot\frac{21}{10}=2-\frac{9}{8}=\frac{7}{8}\).

Ответ: \(\frac{7}{8}\).