481. Выполните действия: a) \(\frac{2}{7} - \frac{1}{8}\), \(\frac{7}{36} + \frac{1}{6}\), \(\frac{19}{45} - \frac{7}{60}\) б) \(\frac{3}{4} - \frac{2}{7}\), \(\frac{8}{9} + \frac{2}{3}\), \(\frac{15}{36} - \frac{7}{60}\) в) \(\frac{8}{9} - \frac{1}{2}\), \(\frac{11}{25} + \frac{4}{5}\), \(\frac{20}{21} - \frac{13}{35}\) г) \(\frac{6}{7} - \frac{1}{6}\), \(\frac{2}{9} + \frac{11}{18}\), \(\frac{21}{50} - \frac{7}{30}\)

Решение: a) \(\frac{2}{7} - \frac{1}{8} = \frac{2 \cdot 8 - 1 \cdot 7}{7 \cdot 8} = \frac{16 - 7}{56} = \frac{9}{56}\) \(\frac{7}{36} + \frac{1}{6} = \frac{7 + 1 \cdot 6}{36} = \frac{7 + 6}{36} = \frac{13}{36}\) \(\frac{19}{45} - \frac{7}{60} = \frac{19 \cdot 4 - 7 \cdot 3}{180} = \frac{76 - 21}{180} = \frac{55}{180} = \frac{11}{36}\) б) \(\frac{3}{4} - \frac{2}{7} = \frac{3 \cdot 7 - 2 \cdot 4}{4 \cdot 7} = \frac{21 - 8}{28} = \frac{13}{28}\) \(\frac{8}{9} + \frac{2}{3} = \frac{8 + 2 \cdot 3}{9} = \frac{8 + 6}{9} = \frac{14}{9}\) \(\frac{15}{36} - \frac{7}{60} = \frac{15 \cdot 5 - 7 \cdot 3}{180} = \frac{75 - 21}{180} = \frac{54}{180} = \frac{3}{10}\) в) \(\frac{8}{9} - \frac{1}{2} = \frac{8 \cdot 2 - 1 \cdot 9}{9 \cdot 2} = \frac{16 - 9}{18} = \frac{7}{18}\) \(\frac{11}{25} + \frac{4}{5} = \frac{11 + 4 \cdot 5}{25} = \frac{11 + 20}{25} = \frac{31}{25}\) \(\frac{20}{21} - \frac{13}{35} = \frac{20 \cdot 5 - 13 \cdot 3}{105} = \frac{100 - 39}{105} = \frac{61}{105}\) г) \(\frac{6}{7} - \frac{1}{6} = \frac{6 \cdot 6 - 1 \cdot 7}{7 \cdot 6} = \frac{36 - 7}{42} = \frac{29}{42}\) \(\frac{2}{9} + \frac{11}{18} = \frac{2 \cdot 2 + 11}{18} = \frac{4 + 11}{18} = \frac{15}{18} = \frac{5}{6}\) \(\frac{21}{50} - \frac{7}{30} = \frac{21 \cdot 3 - 7 \cdot 5}{150} = \frac{63 - 35}{150} = \frac{28}{150} = \frac{14}{75}\)