278. Найдите сумму: a) 7 + 2 5/8; б) 9 1/9 + 20; в) 64 1/7 + 4 4/7; г) 7 5/7 + 4 1/7.

a) $$7 + 2\frac{5}{8} = (7+2) + \frac{5}{8} = 9 + \frac{5}{8} = 9\frac{5}{8}$$ б) $$9\frac{1}{9} + 20 = (9+20) + \frac{1}{9} = 29 + \frac{1}{9} = 29\frac{1}{9}$$ в) $$64\frac{1}{7} + 4\frac{4}{7} = (64+4) + (\frac{1}{7} + \frac{4}{7}) = 68 + \frac{1+4}{7} = 68 + \frac{5}{7} = 68\frac{5}{7}$$ г) $$7\frac{5}{7} + 4\frac{1}{7} = (7+4) + (\frac{5}{7} + \frac{1}{7}) = 11 + \frac{5+1}{7} = 11 + \frac{6}{7} = 11\frac{6}{7}$$ **Ответ:** a) $$9\frac{5}{8}$$, б) $$29\frac{1}{9}$$, в) $$68\frac{5}{7}$$, г) $$11\frac{6}{7}$$