The side of a square is increased from 20cm to 21cm. Calculate the percentage increase in its area

A.
2.5% 
B.
9.3% 
C.
10.0% 
D.
10.25%
Correct Answer: Option D
Explanation
old area = 20^{2} = 400
new area = 21^{2} = 441
% increase in area (=frac{41}{400}times frac{100}{1}\
=10.25%)