Problem: If the radius of a circle is increased 100%, the area is increased:
Answer Choices:
A. 100%
B. 200%
C. 300%
D. 400%
E. by none of these
Solution:
Let r be the original radius; then
2r= new radius, πr2= original area, 4πr2= new area.
Percent increase in area =πr24πr2−πr2​⋅100=300.