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Решение:

1. \( 0,5 : 1,25 + 1 \frac{2}{5} : 1 \frac{4}{7} \) : \( 3 \frac{2}{11} \)
1. \( 0,5 : 1,25 = \frac{1}{2} : \frac{5}{4} = \frac{1}{2} \cdot \frac{4}{5} = \frac{4}{10} = 0,4 \)
2. \( 1 \frac{2}{5} = \frac{7}{5} \), \( 1 \frac{4}{7} = \frac{11}{7} \)
3. \( \frac{7}{5} : \frac{11}{7} = \frac{7}{5} \cdot \frac{7}{11} = \frac{49}{55} \)
4. \( 0,4 + \frac{49}{55} = \frac{2}{5} + \frac{49}{55} = \frac{22}{55} + \frac{49}{55} = \frac{71}{55} \)
5. \( 3 \frac{2}{11} = \frac{35}{11} \)
6. \( \frac{71}{55} : \frac{35}{11} = \frac{71}{55} \cdot \frac{11}{35} = \frac{71}{5 \cdot 35} = \frac{71}{175} \)
2. \( 2 \frac{3}{8} + (14 : 5 - \frac{3}{7} : \frac{9}{14}) : 2 \)
1. \( 14 : 5 = \frac{14}{5} \)
2. \( \frac{3}{7} : \frac{9}{14} = \frac{3}{7} \cdot \frac{14}{9} = \frac{1}{1} \cdot \frac{2}{3} = \frac{2}{3} \)
3. \( \frac{14}{5} - \frac{2}{3} = \frac{42}{15} - \frac{10}{15} = \frac{32}{15} \)
4. \( \frac{32}{15} : 2 = \frac{32}{15} \cdot \frac{1}{2} = \frac{16}{15} \)
5. \( 2 \frac{3}{8} = \frac{19}{8} \)
6. \( \frac{19}{8} + \frac{16}{15} = \frac{19 \cdot 15 + 16 \cdot 8}{120} = \frac{285 + 128}{120} = \frac{413}{120} = 3 \frac{53}{120} \)
3. \( (2 \frac{5}{6} - \frac{3}{7}) : 0,4 \cdot 2 + 3 \frac{4}{7} \cdot 0,28 \)
1. \( 2 \frac{5}{6} = \frac{17}{6} \)
2. \( \frac{17}{6} - \frac{3}{7} = \frac{17 \cdot 7 - 3 \cdot 6}{42} = \frac{119 - 18}{42} = \frac{101}{42} \)
3. \( 0,4 = \frac{2}{5} \)
4. \( \frac{101}{42} : \frac{2}{5} = \frac{101}{42} \cdot \frac{5}{2} = \frac{505}{84} \)
5. \( 3 \frac{4}{7} = \frac{25}{7} \)
6. \( 0,28 = \frac{7}{25} \)
7. \( \frac{25}{7} \cdot \frac{7}{25} = 1 \)
8. \( \frac{505}{84} \cdot 2 + 1 = \frac{505}{42} + 1 = \frac{505 + 42}{42} = \frac{547}{42} = 13 \frac{1}{42} \)

Ответ: 1) \( \frac{71}{175} \); 2) \( 3 \frac{53}{120} \); 3) \( 13 \frac{1}{42} \).