The radius of a spherical balloon is inflated from 7 cm to 10.5 cm. The percentage increase in its surface area is:
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 125%
Initial surface area = 4 × 22/7 × 7 × 7 = 616 cm2
Final surface area = 4 × 22/7 × 10.5 × 10.5 = 1386 cm2.
Increase in the surface area = 1386 - 616 = 770.
% increase = 770/616 × 100 = 125%.