If the surface area of two spheres is in the ratio 81 : 25, then what is the ratio of their radii.

5 : 8 7 : 9 5 : 7 9 : 5

9 : 5

Area             81            :         25 ∴    Radii              9             :         5            *(radii ratio = \(\sqrt {area\;ratio}\)) The ratio of their radii = 9  : 5