To find ratios, both quantities should be in same unit.
$$5$$ to $$50$$ paise
$$\Rightarrow$$ $$5\times 100$$ paise to $$50$$ paise ($$\because$$ $$Rs.1=100paise$$)
$$\Rightarrow$$ $$500$$ paise to $$50$$ paise
Thus, the ratio is $$\cfrac{500}{50}=\cfrac{10}{1}=10:1$$