Question

The radius of a hemispherical balloon increases from 6 cm to 12 cm as air is being pumped into it. The ratios of the surface areas of the balloon in the two cases is 

A. 1 : 4  B. 1 : 3 C. 2 : 3 D. 2 : 1

Answer 1

A. 1 : 4

Radius of hemisphere initially = 6 cm

Radius of hemisphere finally = 12 cm

Surface area of hemisphere = 2 x π x r²

Thus ratio of the surface areas = (2 x π x 6²)/(2 x π x 12²)

= 1/4