277. 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.

Решение:

1. \( 5 \frac{7}{8} + 6 \frac{3}{10} = \frac{47}{8} + \frac{63}{10} = \frac{235}{40} + \frac{252}{40} = \frac{487}{40} = 12 \frac{7}{40} \)
2. \( 6 \frac{3}{8} + 2 \frac{5}{9} = \frac{51}{8} + \frac{23}{9} = \frac{459}{72} + \frac{184}{72} = \frac{643}{72} = 8 \frac{67}{72} \)
3. \( 1 \frac{8}{21} + 4 \frac{3}{14} + 2 \frac{2}{7} = \frac{29}{21} + \frac{59}{14} + \frac{16}{7} = \frac{58}{42} + \frac{177}{42} + \frac{96}{42} = \frac{331}{42} = 7 \frac{37}{42} \)

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