The area of a circle is increased by 300%. By what percent has the radius of the circle increased?  Choices:
A) 400%  B) 200%  C) 100%  D) 600%  E) 800%
The area of the circle is increased by 300%, thus the area is increased 4 times.   The area of a circle it proportional to the square of the radius (area=πr^2), therefore the radius must increase 2 times (diameter increase 2 times = area increase 4 times), which is increase by 100%.   Answer: 100%
<result>C</result>
The area of a circle is increased by 300%. By what percent has the radius of the circle increased?