3. \(\frac{9}{20}\cdot\frac{2}{3}+\frac{5}{14}\cdot\frac{7}{25}\)

\(\frac{9}{20}\cdot\frac{2}{3}=\frac{3}{10}\), \(\frac{5}{14}\cdot\frac{7}{25}=\frac{1}{10}\).

\(\frac{3}{10}+\frac{1}{10}=\frac{4}{10}=\frac{2}{5}\).

Ответ: \(\frac{2}{5}\).