Ответ:

  1. \(\frac{3}{5}\cdot4=\frac{12}{5}=2\frac{2}{5}\).
  2. \(6:\frac{2}{3}=6\cdot\frac{3}{2}=9\).
  3. \(\frac{5}{8}\cdot12=\frac{15}{2}=7\frac{1}{2}\).
  4. \(7:\frac{1}{4}=7\cdot4=28\).
  5. \(\frac{9}{10}:3=\frac{9}{10}\cdot\frac{1}{3}=\frac{3}{10}\).