2 (3 балла) Решите уравнение: a) $$\frac{1}{3}x = \frac{20}{9}$$ b) $$\frac{21}{5}y = \frac{33}{10}$$ c) $$5x = \frac{7}{15}$$

a) $$\frac{1}{3}x = \frac{20}{9}$$ $$x = \frac{20}{9} : \frac{1}{3}$$ $$x = \frac{20}{9} \cdot \frac{3}{1}$$ $$x = \frac{20 \cdot 3}{9 \cdot 1} = \frac{60}{9} = \frac{20}{3} = 6\frac{2}{3}$$ b) $$\frac{21}{5}y = \frac{33}{10}$$ $$y = \frac{33}{10} : \frac{21}{5}$$ $$y = \frac{33}{10} \cdot \frac{5}{21}$$ $$y = \frac{33 \cdot 5}{10 \cdot 21} = \frac{165}{210} = \frac{11}{14}$$ (Сократили на 15) c) $$5x = \frac{7}{15}$$ $$x = \frac{7}{15} : 5$$ $$x = \frac{7}{15} \cdot \frac{1}{5}$$ $$x = \frac{7}{15 \cdot 5} = \frac{7}{75}$$