№5. Выполните действия: а) (10rac{4}{15} + 9rac{11}{15} - 8rac{1}{30}) б) (19rac{1}{17} - 8rac{9}{17} - 3rac{15}{17}) в) ((6rac{7}{12} + 8rac{5}{12}) - (7rac{16}{21} - 4rac{6}{21}))

а) (10rac{4}{15} + 9rac{11}{15} - 8rac{1}{30} = (10+9-8) + (rac{4}{15} + rac{11}{15} - rac{1}{30}) = 11 + rac{8+22-1}{30} = 11 + rac{29}{30} = 11rac{29}{30}) б) (19rac{1}{17} - 8rac{9}{17} - 3rac{15}{17} = (19-8-3) + (rac{1}{17} - rac{9}{17} - rac{15}{17}) = 8 - rac{23}{17} = 8 - 1rac{6}{17} = 7 - rac{6}{17} = 6rac{11}{17}) в) ((6rac{7}{12} + 8rac{5}{12}) - (7rac{16}{21} - 4rac{6}{21}) = (6+8) + (rac{7}{12} + rac{5}{12}) - ((7-4) + (rac{16}{21} - rac{6}{21})) = 14 + rac{12}{12} - (3 + rac{10}{21}) = 15 - 3 - rac{10}{21} = 12 - rac{10}{21} = 11rac{11}{21})