Ответ:

  1. \(\frac{4}{13}:5=\frac{4}{13}\cdot\frac{1}{5}=\frac{4}{65}\).
  2. \(\frac{a}{b}:c=\frac{a}{bc}\).
  3. \(12:\frac{8}{9}=12\cdot\frac{9}{8}=\frac{27}{2}\).
  4. \(a:\frac{b}{c}=\frac{ac}{b}\).