3. Выполните действия: 1) $$12\frac{3}{8} + 8\frac{1}{6}$$; 3) $$11\frac{11}{12} - 5\frac{7}{9}$$ 2) $$3\frac{13}{15} + 6\frac{7}{10}$$; 4) $$9\frac{17}{24} - 8\frac{11}{36}$$

Выполним действия:

1. $$12\frac{3}{8} + 8\frac{1}{6} = 12\frac{9}{24} + 8\frac{4}{24} = (12 + 8) + (\frac{9}{24} + \frac{4}{24}) = 20 + \frac{13}{24} = 20\frac{13}{24}$$
2. $$3\frac{13}{15} + 6\frac{7}{10} = 3\frac{26}{30} + 6\frac{21}{30} = (3 + 6) + (\frac{26}{30} + \frac{21}{30}) = 9 + \frac{47}{30} = 9 + 1\frac{17}{30} = 10\frac{17}{30}$$
3. $$11\frac{11}{12} - 5\frac{7}{9} = 11\frac{33}{36} - 5\frac{28}{36} = (11 - 5) + (\frac{33}{36} - \frac{28}{36}) = 6 + \frac{5}{36} = 6\frac{5}{36}$$
4. $$9\frac{17}{24} - 8\frac{11}{36} = 9\frac{51}{72} - 8\frac{22}{72} = (9 - 8) + (\frac{51}{72} - \frac{22}{72}) = 1 + \frac{29}{72} = 1\frac{29}{72}$$

Ответ: 1) $$20\frac{13}{24}$$; 2) $$10\frac{17}{30}$$; 3) $$6\frac{5}{36}$$; 4) $$1\frac{29}{72}$$