There are two concentric circles with radii 5 and 4. If the radius of the outer circle is increased by 20% and the radius of the inner circle decreased by 50%, by what percent does the area between the circles increase?  Choose one.
A) 56 B) 156 C) 256 D) 356 E) 456
The area of a circle is piR^2, where R is the radius.   The area of the big circle is 25pi.   The area of the small circle is 16pi.   The area A1 between the circles is 9pi.   When the big circle's radius increases, the new area is 36pi.   When the small circle's radius decreases, the new area is 4pi.   The area A2 between the circles is 32pi.   The ratio of A2/A1 is 32/9 = 3.56 which is an increase of 256%.   The answer is 256.
<result>C</result>
There are two concentric circles with radii 5 and 4. If the radius of the outer circle is increased by 20% and the radius of the inner circle decreased by 50%, by what percent does the area between the circles increase?