There are two concentric circles with radii 8 and 4. If the radius of the outer circle is increased by 25% and the radius of the inner circle decreased by 25%, by what percent does the area between the circles increase?
Choose the correct choice from the following:	A) 75	B) 80	C) 85	D) 90	E) 95

Rationale: "the area of a circle is pir ^ 2 , where r is the radius . the area of the big circle is 64 pi . the area of the small circle is 16 pi . the area a 1 between the circles is 48 pi . when the big circle ' s radius increases , the new area is 100 pi . when the small circle ' s radius decreases , the new area is 9 pi . the area a 2 between the circles is 91 pi . the ratio of a 2 / a 1 is 91 / 48 = 1.9 which is an increase of 90 % . the answer is d ."
Answer: D