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
Original AreaNew AreaPercent Increaseβ=Οr2=Ο(2r)2=4Οr2=Original AreaNew AreaβOriginal AreaβΓ100%=Οr24Οr2βΟr2βΓ100%=Οr23Οr2βΓ100%=3Γ100%=300%ββ