There are two concentric circles with radii 6 and 4. If the radius of the outer circle is increased by 50% and the radius of the inner circle decreased by 25%, by what percent does the area between the circles increase?  Choose the correct choice:	A) 160	B) 210	C) 260	D) 310	E) 360
The area of a circle is piR^2, where R is the radius.   The area of the big circle is 36pi.   The area of the small circle is 16pi.   The area A1 between the circles is 20pi.   When the big circle's radius increases, the new area is 81pi.   When the small circle's radius decreases, the new area is 9pi.   The area A2 between the circles is 72pi.   The ratio of A2/A1 is  72/20= 
<gadget id="calculator"> 72/20</gadget>
<output>18/5 = around 3.6</output>
3.6 which is an increase of 260%.   The answer is 260.
<result>C</result>
There are two concentric circles with radii 6 and 4. If the radius of the outer circle is increased by 50% and the radius of the inner circle decreased by 25%, by what percent does the area between the circles increase?