The area of a circle is increased by 300%. By what percent has the diameter of the circle increased?	Pick one:
A) 400%  B) 200%  C) 300%  D) 100%  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 diameter (area=πd^2/4), therefore the diameter must increase 2 times (diameter increase 2 times = area increase 4 times), which is increase by 100%.   Answer: 100%.
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The area of a circle is increased by 300%. By what percent has the diameter of the circle increased?