Выполните действия с дробями: а) 7/8 - 5/6 * 9/20; б) 2/9 + 4/7 : 9/28; в) 2 5/8 : 3/4 + 1/2; г) 1 1/4 + 2/7 - 23/28...

а) $\frac{7}{8} - \frac{5}{6} \cdot \frac{9}{20} = \frac{7}{8} - \frac{1 \cdot 3}{2 \cdot 4} = \frac{7}{8} - \frac{3}{8} = \frac{4}{8} = \frac{1}{2}$ б) $\frac{2}{9} + \frac{4}{7} : \frac{9}{28} = \frac{2}{9} + \frac{4}{7} \cdot \frac{28}{9} = \frac{2}{9} + \frac{4 \cdot 4}{9} = \frac{2}{9} + \frac{16}{9} = \frac{18}{9} = 2$ в) $2\frac{5}{8} : \frac{3}{4} + \frac{1}{2} = \frac{21}{8} \cdot \frac{4}{3} + \frac{1}{2} = \frac{7}{2} + \frac{1}{2} = \frac{8}{2} = 4$ г) $1\frac{1}{4} + \frac{2}{7} - \frac{23}{28} = \frac{5}{4} + \frac{2}{7} - \frac{23}{28} = \frac{35 + 8 - 23}{28} = \frac{20}{28} = \frac{5}{7}$ д) $(\frac{17}{15} - \frac{1}{12}) \cdot \frac{20}{3} = \frac{68 - 5}{60} \cdot \frac{20}{3} = \frac{63}{60} \cdot \frac{20}{3} = \frac{21 \cdot 1}{3 \cdot 1} = 7$ е) $\frac{21}{4} : \frac{49}{64} \cdot \frac{7}{8} = \frac{21}{4} \cdot \frac{64}{49} \cdot \frac{7}{8} = \frac{3 \cdot 16 \cdot 7}{7 \cdot 8} = \frac{3 \cdot 2}{1} = 6$ ж) $\frac{7}{2} : (\frac{7}{8} - \frac{3}{4}) = \frac{7}{2} : (\frac{7 - 6}{8}) = \frac{7}{2} : \frac{1}{8} = \frac{7}{2} \cdot 8 = 28$ з) $\frac{45}{8} \cdot \frac{6}{5} : \frac{9}{4} = \frac{9 \cdot 3}{4} \cdot \frac{4}{9} = 3$ и) $(1\frac{2}{7} - \frac{1}{2}) \cdot 28 = (\frac{9}{7} - \frac{1}{2}) \cdot 28 = \frac{18 - 7}{14} \cdot 28 = \frac{11}{14} \cdot 28 = 22$ к) $1 - \frac{3}{7} : \frac{15}{28} = 1 - \frac{3}{7} \cdot \frac{28}{15} = 1 - \frac{1 \cdot 4}{5} = 1 - \frac{4}{5} = \frac{1}{5}$ л) $\frac{9}{14} : \frac{5}{2} - \frac{4}{35} = \frac{9}{14} \cdot \frac{2}{5} - \frac{4}{35} = \frac{9}{35} - \frac{4}{35} = \frac{5}{35} = \frac{1}{7}$ м) $\frac{32}{7} : \frac{16}{35} \cdot \frac{4}{5} = \frac{32}{7} \cdot \frac{35}{16} \cdot \frac{4}{5} = 2 \cdot 5 \cdot \frac{4}{5} = 8$