The area of a circle is increased by 800%. By what percent has the radius of the circle increased?
Pick:
A) 100%
B) 400%
C) 300%
D) 600%
E) 200%
The area of the circle is increased by 800%, thus the area is increased 9 times.   The area of a circle it proportional to the square of the radius (area=πr^2), therefore the radius must increase 3 times (diameter increase 3 times = area increase 9 times), which is increase by 200%.   Answer: 200%.
<result>E</result>
The area of a circle is increased by 800%. By what percent has the radius of the circle increased?