10 вариант: 1) 7/20 + 2/5; 2) 4 − 8/15; 3) 9 1/6 + 12 1/2; 4) 7 1/10 − 3 1/6; 5) 25/36 × 27/50; 6) 3 2/3 × 3/4; 7) 3/4 : 6; 8) 1 1/3 : 1 7/9.

1. \(\frac{7}{20}+\frac{2}{5}=\frac{7}{20}+\frac{8}{20}=\frac{15}{20}=\frac{3}{4}\).
2. \(4-\frac{8}{15}=\frac{60}{15}-\frac{8}{15}=\frac{52}{15}=3\frac{7}{15}\).
3. \(9\frac{1}{6}+12\frac{1}{2}=21+\frac{1}{6}+\frac{3}{6}=21\frac{4}{6}=21\frac{2}{3}\).
4. \(7\frac{1}{10}-3\frac{1}{6}=\frac{71}{10}-\frac{19}{6}=\frac{213-95}{30}=\frac{118}{30}=3\frac{14}{15}\).
5. \(\frac{25}{36}\times\frac{27}{50}=\frac{1}{2}\times\frac{3}{4}=\frac{3}{8}\).
6. \(3\frac{2}{3}\times\frac{3}{4}=\frac{11}{3}\times\frac{3}{4}=\frac{11}{4}=2\frac{3}{4}\).
7. \(\frac{3}{4}:6=\frac{3}{4}\times\frac{1}{6}=\frac{1}{8}\).
8. \(1\frac{1}{3}:1\frac{7}{9}=\frac{4}{3}:\frac{16}{9}=\frac{4}{3}\times\frac{9}{16}=\frac{3}{4}\).

Ответ: 1) 3/4; 2) 3 7/15; 3) 21 2/3; 4) 3 14/15; 5) 3/8; 6) 2 3/4; 7) 1/8; 8) 3/4.