276. Найдите сумму: 1) 5 7/8 + 6 3/10; 2) 6 3/8 + 2 5/9; 3) 1 8/21 + 4 3/14 + 2 2/7.

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

Ответ: 1) \(12\frac{7}{40}\); 2) \(8\frac{67}{72}\); 3) \(7\frac{37}{42}\).