Решение задания 2

1) $$\frac{\frac{1}{20}+\frac{1}{12}}{\frac{1}{27}} = \frac{\frac{3+5}{60}}{\frac{1}{27}} = \frac{\frac{8}{60}}{\frac{1}{27}} = \frac{2}{15} \cdot 27 = \frac{2 \cdot 9}{5} = \frac{18}{5} = 3.6$$

2) $$\frac{\frac{1}{12}-\frac{1}{21}}{\frac{1}{70}} = \frac{\frac{7-4}{84}}{\frac{1}{70}} = \frac{\frac{3}{84}}{\frac{1}{70}} = \frac{1}{28} \cdot 70 = \frac{10}{4} = \frac{5}{2} = 2.5$$

3) $$\frac{\frac{1}{18}+\frac{1}{45}}{\frac{5}{27}} = \frac{\frac{5+2}{90}}{\frac{5}{27}} = \frac{\frac{7}{90}}{\frac{5}{27}} = \frac{7}{90} \cdot \frac{27}{5} = \frac{7 \cdot 3}{10 \cdot 5} = \frac{21}{50} = 0.42$$