1.  If the diameters of a circle is increased by 100% . Its area is increased by ?
A. 100%
B. 200%
C. 300%
D. 400%

Answer: Option C

Explanation:

Original area = π(d/2)2

= (πd2) / 4

New area = π(2d/2)2

= πd2

Increase in area = (πd2 - πd2/4)

= 3πd2/4

∴ Required increase percent

= [(3πd2)/4 x 4/(πd2) x 100]%

= 300%