Ответ:

  1. \(\frac{5}{7}\cdot15=\frac{75}{7}=10\frac{5}{7}\).
  2. \(12\cdot\frac{3}{8}=\frac{36}{8}=\frac{9}{2}=4\frac{1}{2}\).
  3. \(\frac{4}{8}\cdot40=\frac{1}{2}\cdot40=20\).
  4. \(\frac{1}{25}\cdot25=1\).
  5. \(\frac{5}{9}\cdot\frac{9}{15}=\frac{5}{15}=\frac{1}{3}\).
  6. \(\frac{7}{12}\cdot\frac{24}{21}=\frac{7\cdot2}{21}=\frac{2}{3}\).
  7. \(\frac{3}{11}\cdot\frac{2}{6}=\frac{3}{11}\cdot\frac{1}{3}=\frac{1}{11}\).
  8. \(\frac{10}{4}\cdot\frac{7}{100}=\frac{5}{2}\cdot\frac{7}{100}=\frac{7}{40}\).
  9. \(\frac{45}{4}\cdot\frac{6}{15}=\frac{3\cdot6}{4}=\frac{18}{4}=\frac{9}{2}=4\frac{1}{2}\).
  10. \(\left(\frac{3}{8}\right)^2=\frac{9}{64}\).
  11. \(\left(\frac{11}{5}\right)^2=\frac{121}{25}=4\frac{21}{25}\).
  12. \(\left(\frac{6}{7}\right)^3=\frac{216}{343}\).

Ответ: 1) \(10\frac{5}{7}\); 2) \(4\frac{1}{2}\); 3) 20; 4) 1; 5) \(\frac{1}{3}\); 6) \(\frac{2}{3}\); 7) \(\frac{1}{11}\); 8) \(\frac{7}{40}\); 9) \(4\frac{1}{2}\); 10) \(\frac{9}{64}\); 11) \(4\frac{21}{25}\); 12) \(\frac{216}{343}\).