Ответ:

  1. \(4 \cdot \frac{4}{21}=\frac{16}{21}\).
  2. \(6 \cdot \frac{7}{18}=\frac{42}{18}=\frac{7}{3}=2\frac{1}{3}\).
  3. \(\frac{5}{14} \cdot 28=5 \cdot 2=10\).
  4. \(5\frac{3}{5} \cdot \frac{3}{7}=\frac{28}{5}\cdot\frac{3}{7}=\frac{12}{5}=2\frac{2}{5}\).
  5. \(2\frac{2}{15}\cdot1\frac{9}{16}=\frac{32}{15}\cdot\frac{25}{16}=\frac{10}{3}=3\frac{1}{3}\).
  6. \(1\frac{7}{8}\cdot1\frac{1}{15}\cdot1\frac{7}{16}=\frac{15}{8}\cdot\frac{16}{15}\cdot\frac{23}{16}=\frac{23}{8}=2\frac{7}{8}\).

Ответ: 1) \(\frac{16}{21}\); 2) \(2\frac{1}{3}\); 3) \(10\); 4) \(2\frac{2}{5}\); 5) \(3\frac{1}{3}\); 6) \(2\frac{7}{8}\).