The ratio of the radii of two circles is 1 : 3. Then the ratio of their areas is :

Answer: Option C

Let the radii of the two circle be r and 3r respectively.
Then, required ratio :
$$=\frac{\pi r^2}{\pi {\left(3r\right)}^2}=\frac{\pi r^2}{9\pi r^2}=1:9$$