Ответ:

  1. \(\frac{5}{7}\cdot\frac{7}{9}=\frac{35}{63}=\frac{5}{9}\).
  2. \(\frac{1}{20}\cdot\frac{17}{30}=\frac{17}{600}\).
  3. \(\frac{2}{9}\cdot\frac{1}{6}=\frac{2}{54}=\frac{1}{27}\).
  4. \(\frac{5}{6}\cdot\frac{3}{4}=\frac{15}{24}=\frac{5}{8}\).
  5. \(\frac{8}{38}\cdot\frac{4}{19}=\frac{32}{722}=\frac{16}{361}\).
  6. \(\frac{7}{9}\cdot\frac{8}{11}=\frac{56}{99}\).
  7. \(\frac{8}{25}\cdot\frac{7}{20}=\frac{56}{500}=\frac{14}{125}\).
  8. \(\frac{5}{12}\cdot\frac{4}{5}=\frac{20}{60}=\frac{1}{3}\).

Ответ: 1) \(\frac{5}{9}\); 2) \(\frac{17}{600}\); 3) \(\frac{1}{27}\); 4) \(\frac{5}{8}\); 5) \(\frac{16}{361}\); 6) \(\frac{56}{99}\); 7) \(\frac{14}{125}\); 8) \(\frac{1}{3}\).