Two cubes have their volumes in the ratio 1 : 27. Find the ratio of their surface areas.        

Correct Answer : D.

Let their edges be a and b. Then,

   a³/b³ = 1/27 (or) (a/b)³ = (1/3)³ (or) (a/b) = (1/3).

   Ratio of their surface area = 6a²/6b² = a²/b² = (a/b)² = 1/9, = 1:9.