17/20 : 10/34 : 5/2 =

$$\frac{17}{20} : \frac{10}{34} : \frac{5}{2} = \frac{17}{20} \cdot \frac{34}{10} \cdot \frac{2}{5} = \frac{17}{20} \cdot \frac{17}{5} \cdot \frac{2}{5} = \frac{17 \cdot 17 \cdot 2}{20 \cdot 5 \cdot 5} = \frac{578}{500} = \frac{289}{250}$$