Решение:

1. $$\frac{5}{6} + \frac{2}{7} = \frac{5 \cdot 7 + 2 \cdot 6}{6 \cdot 7} = \frac{35 + 12}{42} = \frac{47}{42} = 1\frac{5}{42}$$
2. $$\frac{11}{15} - \frac{3}{5} = \frac{11}{15} - \frac{3 \cdot 3}{5 \cdot 3} = \frac{11}{15} - \frac{9}{15} = \frac{11 - 9}{15} = \frac{2}{15}$$
3. $$\frac{15}{16} - \frac{3}{4} = \frac{15}{16} - \frac{3 \cdot 4}{4 \cdot 4} = \frac{15}{16} - \frac{12}{16} = \frac{15 - 12}{16} = \frac{3}{16}$$
4. $$\frac{3}{20} + \frac{7}{15} = \frac{3 \cdot 3 + 7 \cdot 4}{60} = \frac{9 + 28}{60} = \frac{37}{60}$$
5. $$\frac{13}{16} - \frac{7}{12} = \frac{13 \cdot 3 - 7 \cdot 4}{48} = \frac{39 - 28}{48} = \frac{11}{48}$$
6. $$\frac{9}{14} + \frac{2}{21} = \frac{9 \cdot 3 + 2 \cdot 2}{42} = \frac{27 + 4}{42} = \frac{31}{42}$$
7. $$\frac{19}{36} - \frac{11}{48} = \frac{19 \cdot 4 - 11 \cdot 3}{144} = \frac{76 - 33}{144} = \frac{43}{144}$$
8. $$3\frac{7}{9} + 5\frac{1}{6} = 3 + \frac{7}{9} + 5 + \frac{1}{6} = 8 + \frac{7}{9} + \frac{1}{6} = 8 + \frac{7 \cdot 2 + 1 \cdot 3}{18} = 8 + \frac{14 + 3}{18} = 8 + \frac{17}{18} = 8\frac{17}{18}$$
9. $$3 + 4\frac{1}{7} = 3 + 4 + \frac{1}{7} = 7 + \frac{1}{7} = 7\frac{1}{7}$$
10. $$3\frac{1}{8} + \frac{3}{4} = 3 + \frac{1}{8} + \frac{3}{4} = 3 + \frac{1 + 3 \cdot 2}{8} = 3 + \frac{1 + 6}{8} = 3 + \frac{7}{8} = 3\frac{7}{8}$$