Решение:

1. a) $$6\frac{3}{4}-2\frac{5}{6}-1\frac{3}{8} = 6\frac{18}{24}-2\frac{20}{24}-1\frac{9}{24} = 5\frac{42}{24} - 2\frac{20}{24} - 1\frac{9}{24} = 3\frac{13}{24}$$
2. б) $$9\frac{8}{15}-4\frac{1}{12}+3\frac{7}{20} = 9\frac{32}{60}-4\frac{5}{60}+3\frac{21}{60} = 8\frac{92}{60}$$
3. в) $$7\frac{5}{8}+3\frac{2}{3}-8\frac{3}{16} = 7\frac{15}{24}+3\frac{16}{24}-8\frac{4}{24} = 2\frac{27}{24}= 2\frac{9}{8}=3\frac{1}{8}$$
4. г) $$9\frac{23}{25}-4\frac{7}{10}-2\frac{1}{5}= 9\frac{46}{50}-4\frac{35}{50}-2\frac{10}{50} = 3\frac{1}{50}$$
5. д) $$20-(3\frac{1}{6}+2\frac{3}{4})=20-(3\frac{2}{12}+2\frac{9}{12})=20-(5\frac{11}{12})=14\frac{1}{12}$$
6. e) $$1\frac{5}{6}+(3-1\frac{7}{10})=1\frac{5}{6}+(3-1\frac{7}{10})=1\frac{5}{6}+(2\frac{10}{10}-1\frac{7}{10})=1\frac{5}{6}+1\frac{3}{10}=1\frac{25}{30}+1\frac{9}{30}=2\frac{34}{30}=3\frac{4}{30}$$

Ответ:

1. a) $$3\frac{13}{24}$$
2. б) $$8\frac{92}{60}$$
3. в) $$3\frac{1}{8}$$
4. г) $$3\frac{1}{50}$$
5. д) $$14\frac{1}{12}$$
6. e) $$3\frac{4}{30}$$