Найдите сумму: 1) \( 5 \frac{7}{8} + 6 \frac{3}{10} \); 2) \( 6 \frac{3}{8} + 2 \frac{5}{9} \); 3) \( 1 \frac{8}{21} + 4 \frac{3}{14} + 2 \frac{2}{7} \)

1) **Решение \( 5 \frac{7}{8} + 6 \frac{3}{10} \):** \( 5 \frac{7}{8} + 6 \frac{3}{10} = (5 + 6) + (\frac{7}{8} + \frac{3}{10}) = 11 + (\frac{7 \cdot 5}{8 \cdot 5} + \frac{3 \cdot 4}{10 \cdot 4}) = 11 + (\frac{35}{40} + \frac{12}{40}) = 11 + \frac{47}{40} = 11 + 1 \frac{7}{40} = 12 \frac{7}{40} \) 2) **Решение \( 6 \frac{3}{8} + 2 \frac{5}{9} \):** \( 6 \frac{3}{8} + 2 \frac{5}{9} = (6 + 2) + (\frac{3}{8} + \frac{5}{9}) = 8 + (\frac{3 \cdot 9}{8 \cdot 9} + \frac{5 \cdot 8}{9 \cdot 8}) = 8 + (\frac{27}{72} + \frac{40}{72}) = 8 + \frac{67}{72} = 8 \frac{67}{72} \) 3) **Решение \( 1 \frac{8}{21} + 4 \frac{3}{14} + 2 \frac{2}{7} \):** \( 1 \frac{8}{21} + 4 \frac{3}{14} + 2 \frac{2}{7} = (1 + 4 + 2) + (\frac{8}{21} + \frac{3}{14} + \frac{2}{7}) = 7 + (\frac{8 \cdot 2}{21 \cdot 2} + \frac{3 \cdot 3}{14 \cdot 3} + \frac{2 \cdot 6}{7 \cdot 6}) = 7 + (\frac{16}{42} + \frac{9}{42} + \frac{12}{42}) = 7 + \frac{37}{42} = 7 \frac{37}{42} \) **Ответ:** 1) \( 12 \frac{7}{40} \) 2) \( 8 \frac{67}{72} \) 3) \( 7 \frac{37}{42} \)