The radius of a sphere is increased by 10%. The surface area increases by? Choose the correct choice from the following answers.
A) 21 %
B) 31 %
C) 41 %
D) 51 %
E) none of these

Rationale: since 4 x pi x radius x radius = surface area . therefore , net % change in area = ( x + y + xy / 100 ) % = [ 10 + 10 + ( 10 x 10 ) / 100 ] % or 21 % . answer : a
Answer: A