a) 2\frac{1}{5}:1\frac{7}{20}\cdot\frac{9}{22};

a) $$2\frac{1}{5}:1\frac{7}{20}\cdot\frac{9}{22}=\frac{11}{5}:\frac{27}{20}\cdot\frac{9}{22}=\frac{11}{5}\cdot\frac{20}{27}\cdot\frac{9}{22}=\frac{1\cdot4\cdot1}{1\cdot3\cdot2}=\frac{4}{6}=\frac{2}{3}$$

Ответ: $$\frac{2}{3}$$