3. Умножение и деление обыкновенных дробей: 1) 5/6 · 3/20; 2) 3/7 · 6/11; 3) 10/11 · 11/26; 4) 19/42 · 21/38; 5) 3/4 : 33/20; 6) 25/72 : 45/63; 7) 8/15 : 24; 8) 8 : 4/5; 9) 2/3 · 6/7 : 4/7; 10) 11/12 : 7/24 · 21/22.

1. \(\frac56\cdot\frac3{20}=\frac{15}{120}=\frac18\).
2. \(\frac37\cdot\frac6{11}=\frac{18}{77}\).
3. \(\frac{10}{11}\cdot\frac{11}{26}=\frac5{13}\).
4. \(\frac{19}{42}\cdot\frac{21}{38}=\frac{19}{76}=\frac14\).
5. \(\frac34:\frac{33}{20}=\frac34\cdot\frac{20}{33}=\frac5{11}\).
6. \(\frac{25}{72}:\frac{45}{63}=\frac{25}{72}\cdot\frac{63}{45}=\frac{35}{72}\).
7. \(\frac8{15}:24=\frac8{15}\cdot\frac1{24}=\frac1{45}\).
8. \(8:\frac45=8\cdot\frac54=10\).
9. \(\frac23\cdot\frac67:\frac47=\frac47\cdot\frac74=1\).
10. \(\frac{11}{12}:\frac7{24}\cdot\frac{21}{22}=\frac{11}{12}\cdot\frac{24}{7}\cdot\frac{21}{22}=\frac32\).

Ответ: 1) \(\frac18\); 2) \(\frac{18}{77}\); 3) \(\frac5{13}\); 4) \(\frac14\); 5) \(\frac5{11}\); 6) \(\frac{35}{72}\); 7) \(\frac1{45}\); 8) \(10\); 9) \(1\); 10) \(\frac32\).