9:18 19

$${\frac{9}{19}} : 18 = {\frac{9}{19}} \cdot {\frac{1}{18}} = {\frac{9}{19 \cdot 18}} = {\frac{9}{19 \cdot 9 \cdot 2}} = {\frac{1}{19 \cdot 2}} = {\frac{1}{38}}$$

Ответ: $$\frac{1}{38}$$