4. Выполните умножение: a) \(\frac{3}{7} \cdot \frac{2}{5}\) б) \(\frac{7}{13} \cdot \frac{39}{56}\) в) \(3\frac{1}{9} \cdot \frac{1}{7}\) г) \(2\frac{1}{7} \cdot \frac{4}{5}\) д) \(1\frac{3}{9} \cdot \frac{1}{10}\) е) \(\frac{4}{11} \cdot \frac{7}{12}\)

Решение:

1. а) \( \frac{3}{7} \cdot \frac{2}{5} = \frac{3 \cdot 2}{7 \cdot 5} = \frac{6}{35} \)
2. б) \( \frac{7}{13} \cdot \frac{39}{56} = \frac{7}{13} \cdot \frac{13 \cdot 3}{7 \cdot 8} = \frac{3}{8} \)
3. в) \( 3\frac{1}{9} \cdot \frac{1}{7} = \frac{3 \cdot 9 + 1}{9} \cdot \frac{1}{7} = \frac{28}{9} \cdot \frac{1}{7} = \frac{4 \cdot 7}{9} \cdot \frac{1}{7} = \frac{4}{9} \)
4. г) \( 2\frac{1}{7} \cdot \frac{4}{5} = \frac{2 \cdot 7 + 1}{7} \cdot \frac{4}{5} = \frac{15}{7} \cdot \frac{4}{5} = \frac{3 \cdot 5}{7} \cdot \frac{4}{5} = \frac{12}{7} = 1\frac{5}{7} \)
5. д) \( 1\frac{3}{9} \cdot \frac{1}{10} = 1\frac{1}{3} \cdot \frac{1}{10} = \frac{1 \cdot 3 + 1}{3} \cdot \frac{1}{10} = \frac{4}{3} \cdot \frac{1}{10} = \frac{2 \cdot 2}{3} \cdot \frac{1}{5 \cdot 2} = \frac{2}{15} \)
6. е) \( \frac{4}{11} \cdot \frac{7}{12} = \frac{4}{11} \cdot \frac{7}{4 \cdot 3} = \frac{7}{33} \)

Ответ: а) \(\frac{6}{35}\); б) \(\frac{3}{8}\); в) \(\frac{4}{9}\); г) \(1\frac{5}{7}\); д) \(\frac{2}{15}\); е) \(\frac{7}{33}\).