Ответ:

  1. \(18\cdot\frac{1}{3}-18\cdot\frac{1}{9}=6-2=4\).
  2. \(2\cdot20-\frac{3}{4}\cdot20-\frac{4}{5}\cdot20=40-15-16=9\).
  3. \(18-6-3-2=7\).
  4. \(\frac{5}{6}\cdot\frac{18}{25}+\frac{5}{9}\cdot\frac{18}{25}=\frac{3}{5}+\frac{2}{5}=1\).