Ответ:

  1. а) \(\frac{6}{5}:\left(\frac{9}{10}-\frac{1}{5}\right)=\frac{6}{5}:\frac{7}{10}=\frac{12}{7}\).
  2. б) \(\left(\frac{7}{25}+\frac{1}{5}\right):\frac{3}{50}=\frac{12}{25}\cdot\frac{50}{3}=8\).
  3. в) \(1-\frac{3}{7}:\frac{15}{28}=1-\frac{3}{7}\cdot\frac{28}{15}=1-\frac{4}{5}=\frac{1}{5}\).
  4. г) \(\frac{34}{9}:\frac{17}{54}\cdot\frac{5}{6}=\frac{34}{9}\cdot\frac{54}{17}\cdot\frac{5}{6}=20\).

Ответ: а) \(\frac{12}{7}\); б) 8; в) \(\frac{1}{5}\); г) 20.