Ответ:

  1. \(\frac{3.4}{1-\frac{1}{18}}=\frac{\frac{17}{5}}{\frac{17}{18}}=\frac{18}{5}=3.6\).
  2. \(\frac{0.8}{1+\frac{1}{7}}=\frac{\frac{4}{5}}{\frac{8}{7}}=\frac{7}{10}=0.7\).
  3. \(40\cdot\left(\frac{1}{8}\right)^2-13\cdot\frac{1}{8}=\frac{5}{8}-\frac{13}{8}=-1\).

Ответ: 1) 3,6; 2) 0,7; 3) −1.