20 Вычислите: a) \(\frac{5}{13} + \frac{2}{13} - \frac{4}{13}\); б) \(\frac{7}{21} + \frac{12}{21} - \frac{9}{21}\); в) \(\frac{12}{22} - \frac{5}{22} - \frac{5}{22}\); г) \(\frac{25}{53} - \frac{10}{53}\)

a) \(\frac{5}{13} + \frac{2}{13} - \frac{4}{13} = \frac{5+2-4}{13} = \frac{3}{13}\)

б) \(\frac{7}{21} + \frac{12}{21} - \frac{9}{21} = \frac{7+12-9}{21} = \frac{10}{21}\)

в) \(\frac{12}{22} - \frac{5}{22} - \frac{5}{22} = \frac{12-5-5}{22} = \frac{2}{22} = \frac{1}{11}\)

г) \(\frac{25}{53} - \frac{10}{53} = \frac{25-10}{53} = \frac{15}{53}\)

Ответ: а) \(\frac{3}{13}\), б) \(\frac{10}{21}\), в) \(\frac{1}{11}\), г) \(\frac{15}{53}\)