The radius of a spherical balloon increases from 7 cm to 14 cm as air is being pumped into it. Find the ratio of surface areas of the balloon in the two cases
Radius (r1) of spherical balloon = 7 cm
Radius (r2) of spherical balloon, when air is pumped into it = 14 cm
Ratio = 
= 
= (
)2
= (
)2 = 
Therefore, the ratio between the surface areas is 1:4
18