Решение:

а) $$1\frac{1}{9} - \frac{2}{3} = \frac{10}{9} - \frac{2}{3} = \frac{10}{9} - \frac{6}{9} = \frac{4}{9}$$

б) $$12\frac{3}{8} - 6\frac{7}{20} = 12\frac{15}{40} - 6\frac{14}{40} = 6\frac{1}{40}$$

в) $$4\frac{5}{21} + 5\frac{3}{14} = 4\frac{10}{42} + 5\frac{9}{42} = 9\frac{19}{42}$$

д) $$\frac{3}{10} \cdot \frac{20}{21} = \frac{3 \cdot 20}{10 \cdot 21} = \frac{60}{210} = \frac{6}{21} = \frac{2}{7}$$

е) $$9\frac{1}{3} \cdot 1\frac{1}{8} = \frac{28}{3} \cdot \frac{9}{8} = \frac{28 \cdot 9}{3 \cdot 8} = \frac{252}{24} = \frac{63}{6} = \frac{21}{2} = 10\frac{1}{2}$$

ж) $$\frac{9}{14} : \frac{18}{35} = \frac{9}{14} \cdot \frac{35}{18} = \frac{9 \cdot 35}{14 \cdot 18} = \frac{315}{252} = \frac{5}{4} = 1\frac{1}{4}$$

з) $$3\frac{1}{5} : 2\frac{2}{15} = \frac{16}{5} : \frac{32}{15} = \frac{16}{5} \cdot \frac{15}{32} = \frac{16 \cdot 15}{5 \cdot 32} = \frac{240}{160} = \frac{3}{2} = 1\frac{1}{2}$$