3:9 10

$${\frac{3}{10}} : 9 = {\frac{3}{10}} \cdot {\frac{1}{9}} = {\frac{3}{10 \cdot 9}} = {\frac{3}{10 \cdot 3 \cdot 3}} = {\frac{1}{10 \cdot 3}} = {\frac{1}{30}}$$

Ответ: $$\frac{1}{30}$$