11) \(3\frac{1}{2}:(\frac{4}{15}+2\frac{9}{10})\)

\(3\frac{1}{2}=\frac{7}{2}\), \(2\frac{9}{10}=\frac{29}{10}\).

\(\frac{7}{2}:\left(\frac{4}{15}+\frac{29}{10}\right)=\frac{7}{2}:\frac{19}{6}=\frac{7}{2}\cdot\frac{6}{19}=\frac{21}{19}\).

Ответ: \(\frac{21}{19}\).