Ответ:

  1. \(4\cdot\frac{5}{21}=\frac{20}{21}\).

  2. \(24\cdot\frac{7}{12}=2\cdot7=14\).

  3. \(\frac{16}{63}\cdot9=\frac{16}{7}=2\frac{2}{7}\).

  4. \(36\cdot\frac{13}{48}=\frac{3}{4}\cdot13=\frac{39}{4}=9\frac{3}{4}\).

Ответ: 1) 20/21; 2) 14; 3) 2 2/7; 4) 9 3/4.