5. Сократите: \(\frac{9}{15}\cdot\frac{8}{56}\); \(\frac{42}{90}\); \(\frac{38\cdot18}{9\cdot19}\).

Сократим общие множители:

\(\frac{9}{15}\cdot\frac{8}{56}=\frac{3}{5}\cdot\frac{1}{7}=\frac{3}{35}\).

\(\frac{42}{90}=\frac{7}{15}\).

\(\frac{38\cdot18}{9\cdot19}=\frac{2\cdot18}{9}=4\).

Ответ: \(\frac{3}{35};\ \frac{7}{15};\ 4\).