20. Вычислите: 18$$\cdot\frac{5}{81} - \frac{2}{3}$$. 22. Вычислите: $$\frac{18}{35} : 12 + \frac{1}{10}$$.

20. $$\begin{aligned} 18 \cdot \frac{5}{81} - \frac{2}{3} &= \frac{18}{1} \cdot \frac{5}{81} - \frac{2}{3} = \frac{18 \cdot 5}{1 \cdot 81} - \frac{2}{3} = \frac{90}{81} - \frac{2}{3} = \frac{10}{9} - \frac{2}{3} = \frac{10}{9} - \frac{2 \cdot 3}{3 \cdot 3} = \frac{10}{9} - \frac{6}{9} = \frac{10-6}{9} = \frac{4}{9} \end{aligned}$$ Ответ: $$\frac{\bf{4}}{\bf{9}}$$ 22. $$\begin{aligned} \frac{18}{35} : 12 + \frac{1}{10} &= \frac{18}{35} : \frac{12}{1} + \frac{1}{10} = \frac{18}{35} \cdot \frac{1}{12} + \frac{1}{10} = \frac{18 \cdot 1}{35 \cdot 12} + \frac{1}{10} = \frac{18}{420} + \frac{1}{10} = \frac{3}{70} + \frac{1}{10} = \frac{3}{70} + \frac{1 \cdot 7}{10 \cdot 7} = \frac{3}{70} + \frac{7}{70} = \frac{3+7}{70} = \frac{10}{70} = \frac{1}{7} \end{aligned}$$ Ответ: $$\frac{\bf{1}}{\bf{7}}$$