1. Выполните действия: a) 15/21 + 8/21 + 4/21 б) 3 5/9 + 4 4/9 в) 8 5/12 - 3 10/12 г) 6 5/12 - 2 2/12

a) \(\frac{15}{21} + \frac{8}{21} + \frac{4}{21} = \frac{15 + 8 + 4}{21} = \frac{27}{21} = \frac{9}{7} = 1 \frac{2}{7}\) б) \(3 \frac{5}{9} + 4 \frac{4}{9} = (3 + 4) + (\frac{5}{9} + \frac{4}{9}) = 7 + \frac{9}{9} = 7 + 1 = 8\) в) \(8 \frac{5}{12} - 3 \frac{10}{12} = 8 \frac{5}{12} - 3 \frac{10}{12} = (7 + 1 \frac{5}{12}) - 3 \frac{10}{12} = 7 \frac{17}{12} - 3 \frac{10}{12} = (7 - 3) + (\frac{17}{12} - \frac{10}{12}) = 4 + \frac{7}{12} = 4 \frac{7}{12}\) г) \(6 \frac{5}{12} - 2 \frac{2}{12} = (6 - 2) + (\frac{5}{12} - \frac{2}{12}) = 4 + \frac{3}{12} = 4 + \frac{1}{4} = 4 \frac{1}{4}\)