Question

The radius of a hemispherical balloon increases from 6 cm to 12 cm as air is being pumped into it. The ratio of the surface areas of the balloons in two cases is
(a) 1 : 4
(b) 1 : 3
(c) 2 : 3
(d) 1 : 2

Answer 1

(a) 1 : 4
Ratio of the surface areas of balloon = $\frac{2\mathrm{\pi }\times 6^2}{2\mathrm{\pi }\times {12}^2}=\frac{36}{144}=\frac{1}{4}$