. Вычислите: 1) $$7\frac{2}{7}+2\frac{3}{8}$$; 2) $$6\frac{5}{6}-4\frac{4}{9}$$; 3) $$3\frac{1}{8}+2\frac{5}{6}$$; 4) $$12\frac{11}{12}-3\frac{7}{18}$$; 5) $$4\frac{3}{5}\cdot 12\frac{5}{6}$$; 6) $$7\frac{1}{6}\div 8\frac{1}{7}$$; 7) $$40\frac{21}{40}\cdot \frac{3}{4}$$.

1) $$7\frac{2}{7}+2\frac{3}{8} = 7 + 2 + \frac{2}{7} + \frac{3}{8} = 9 + \frac{2\cdot 8 + 3 \cdot 7}{56} = 9 + \frac{16 + 21}{56} = 9 + \frac{37}{56} = 9\frac{37}{56}$$

2) $$6\frac{5}{6}-4\frac{4}{9} = 6 - 4 + \frac{5}{6} - \frac{4}{9} = 2 + \frac{5\cdot 3 - 4 \cdot 2}{18} = 2 + \frac{15 - 8}{18} = 2 + \frac{7}{18} = 2\frac{7}{18}$$

3) $$3\frac{1}{8}+2\frac{5}{6} = 3 + 2 + \frac{1}{8} + \frac{5}{6} = 5 + \frac{1\cdot 3 + 5 \cdot 4}{24} = 5 + \frac{3 + 20}{24} = 5 + \frac{23}{24} = 5\frac{23}{24}$$

4) $$12\frac{11}{12}-3\frac{7}{18} = 12 - 3 + \frac{11}{12} - \frac{7}{18} = 9 + \frac{11\cdot 3 - 7 \cdot 2}{36} = 9 + \frac{33 - 14}{36} = 9 + \frac{19}{36} = 9\frac{19}{36}$$

5) $$4\frac{3}{5}\cdot 12\frac{5}{6} = \frac{4\cdot 5 + 3}{5} \cdot \frac{12\cdot 6 + 5}{6} = \frac{23}{5} \cdot \frac{77}{6} = \frac{23 \cdot 77}{5 \cdot 6} = \frac{1771}{30} = 59\frac{1}{30}$$

6) $$7\frac{1}{6}\div 8\frac{1}{7} = \frac{7\cdot 6 + 1}{6} \div \frac{8\cdot 7 + 1}{7} = \frac{43}{6} \div \frac{57}{7} = \frac{43}{6} \cdot \frac{7}{57} = \frac{43 \cdot 7}{6 \cdot 57} = \frac{301}{342}$$

7) $$40\frac{21}{40}\cdot \frac{3}{4} = \frac{40\cdot 40 + 21}{40} \cdot \frac{3}{4} = \frac{1600 + 21}{40} \cdot \frac{3}{4} = \frac{1621}{40} \cdot \frac{3}{4} = \frac{1621 \cdot 3}{40 \cdot 4} = \frac{4863}{160} = 30\frac{63}{160}$$

Ответ: 1) $$9\frac{37}{56}$$; 2) $$2\frac{7}{18}$$; 3) $$5\frac{23}{24}$$; 4) $$9\frac{19}{36}$$; 5) $$59\frac{1}{30}$$; 6) $$\frac{301}{342}$$; 7) $$30\frac{63}{160}$$.