7) 12/(20·3) =; 8) 27/(5·4) =; 9) 8/(5·4) =; 10) 21/5 : 6/7 =; 11) 3/5 : 4/35 =; 12) 4/5 : 2/7 =

1. \(\frac{12}{20\cdot3}=\frac{12}{60}=\frac{1}{5}=0.2\).
2. \(\frac{27}{5\cdot4}=\frac{27}{20}=1\frac{7}{20}\).
3. \(\frac{8}{5\cdot4}=\frac{8}{20}=\frac{2}{5}=0.4\).
4. \(\frac{21}{5}:\frac{6}{7}=\frac{21}{5}\cdot\frac{7}{6}=\frac{49}{10}=4.9\).
5. \(\frac{3}{5}:\frac{4}{35}=\frac{3}{5}\cdot\frac{35}{4}=\frac{21}{4}=5\frac{1}{4}\).
6. \(\frac{4}{5}:\frac{2}{7}=\frac{4}{5}\cdot\frac{7}{2}=\frac{14}{5}=2.8\).

Ответ: 7) 0.2; 8) 1 7/20; 9) 0.4; 10) 4.9; 11) 5 1/4; 12) 2.8.