There are two concentric circles with radii 8 and 6. If the radius of the outer circle is increased by 25% and the radius of the inner circle decreased by 50%, by what percent does the area between the circles increase?
Answers:
A) 225 B) 250 C) 275 D) 300 E) 325
The area of a circle is piR^2, where R is the radius.   The area of the big circle is 64pi.   The area of the small circle is 36pi.   The area A1 between the circles is 28pi.   When the big circle's radius increases, the new area is 100pi.   When the small circle's radius decreases, the new area is 9pi.   The area A2 between the circles is 91pi.   The ratio of A2/A1 is  91/28= 
<gadget id="calculator"> 91/28</gadget>
<output>13/4 = around 3.25</output>
3.25 which is an increase of 225%.   The answer is 225.
<result>A</result>
There are two concentric circles with radii 8 and 6. If the radius of the outer circle is increased by 25% and the radius of the inner circle decreased by 50%, by what percent does the area between the circles increase?