② a) \(12\frac{3}{8}+8\frac{1}{6}\) б) \(3\frac{13}{15}+6\frac{7}{10}\) в) \(9\frac{8}{21}+4\frac{11}{14}\) г) \(8\frac{5}{9}+7\frac{3}{4}+12\frac{7}{12}\)

a) \(12\frac{3}{8}+8\frac{1}{6}\) = \((12 + 8) + (\frac{3}{8} + \frac{1}{6})\) = \(20 + (\frac{3*3}{8*3} + \frac{1*4}{6*4})\) = \(20 + (\frac{9}{24} + \frac{4}{24})\) = \(20 + \frac{13}{24}\) = \(20\frac{13}{24}\)

Ответ: \(20\frac{13}{24}\)

б) \(3\frac{13}{15}+6\frac{7}{10}\) = \((3+6) + (\frac{13}{15} + \frac{7}{10})\) = \(9 + (\frac{13*2}{15*2} + \frac{7*3}{10*3})\) = \(9 + (\frac{26}{30} + \frac{21}{30})\) = \(9 + \frac{47}{30}\) = \(9 + \frac{30+17}{30}\) = \(9 + 1\frac{17}{30}\) = \(10\frac{17}{30}\)

Ответ: \(10\frac{17}{30}\)

в) \(9\frac{8}{21}+4\frac{11}{14}\) = \((9+4) + (\frac{8}{21} + \frac{11}{14})\) = \(13 + (\frac{8*2}{21*2} + \frac{11*3}{14*3})\) = \(13 + (\frac{16}{42} + \frac{33}{42})\) = \(13 + \frac{49}{42}\) = \(13 + \frac{42+7}{42}\) = \(13 + 1\frac{7}{42}\) = \(14\frac{7}{42}\) = \(14\frac{1}{6}\)

Ответ: \(14\frac{1}{6}\)

г) \(8\frac{5}{9}+7\frac{3}{4}+12\frac{7}{12}\) = \((8+7+12) + (\frac{5}{9} + \frac{3}{4} + \frac{7}{12})\) = \(27 + (\frac{5*4}{9*4} + \frac{3*9}{4*9} + \frac{7*3}{12*3})\) = \(27 + (\frac{20}{36} + \frac{27}{36} + \frac{21}{36})\) = \(27 + \frac{20+27+21}{36}\) = \(27 + \frac{68}{36}\) = \(27 + \frac{36+32}{36}\) = \(27 + 1\frac{32}{36}\) = \(28\frac{32}{36}\) = \(28\frac{8}{9}\)

Ответ: \(28\frac{8}{9}\)