П.20 Выполните действие: a) $$\frac{16}{27} \cdot \frac{9}{4}$$; б) $$\frac{42}{5} \cdot \frac{55}{7}$$; в) $$\frac{7}{12} : \frac{3}{12}$$; г) $$\frac{14}{55} : \frac{7}{22}$$

**П.20 Решение:** a) $$\frac{16}{27} \cdot \frac{9}{4} = \frac{16 \cdot 9}{27 \cdot 4} = \frac{4 \cdot 1}{3 \cdot 1} = \frac{4}{3} = 1\frac{1}{3}$$ б) $$\frac{42}{5} \cdot \frac{55}{7} = \frac{42 \cdot 55}{5 \cdot 7} = \frac{6 \cdot 11}{1 \cdot 1} = 66$$ в) $$\frac{7}{12} : \frac{3}{12} = \frac{7}{12} \cdot \frac{12}{3} = \frac{7 \cdot 12}{12 \cdot 3} = \frac{7}{3} = 2\frac{1}{3}$$ г) $$\frac{14}{55} : \frac{7}{22} = \frac{14}{55} \cdot \frac{22}{7} = \frac{14 \cdot 22}{55 \cdot 7} = \frac{2 \cdot 2}{5 \cdot 1} = \frac{4}{5}$$