① $$18 \cdot (\frac{1}{3})^2 - 20 \cdot \frac{1}{9} = 18 \cdot \frac{1}{9} - \frac{20}{9} = \frac{18}{9} - \frac{20}{9} = \frac{18-20}{9} = \frac{-2}{9} = -\frac{2}{9}$$.
Ответ: $$-\frac{2}{9}$$