50. Вычислите: \(13-(3-1\frac{20}{21}):\frac4{49}+\frac3{10}\).

\(3-1\frac{20}{21}=3-\frac{41}{21}=\frac{22}{21}\).

\(\frac{22}{21}:\frac4{49}=\frac{22}{21}\cdot\frac{49}{4}=\frac{77}{6}\).

\(13-\frac{77}{6}+\frac3{10}=\frac{390-385+9}{30}=\frac{14}{15}\).

Ответ: \(\frac{14}{15}\).