The area of a circle is increased by 300%. By what percent has the diameter of the circle increased?	Answers.
A) 400 %
B) 200 %
C) 300 %
D) 100 %
E) 800 %

Rationale: 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 = π d ^ 2 / 4 ) , therefore the diameter must increase 2 times ( diameter increase 2 times = area increase 4 times ) , which is increase by 100 % . answer : d .
Answer: D