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Rings

by sampath » Fri Jul 22, 2011 1:36 am
If a ring is formed by the inner circle of radius 2 and the outer circle of radius
3, what is the ratio of the area of the ring to that of the inner circle?

Is the answer [spoiler](9/4)[/spoiler]?

Thanks in advance.
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by knight247 » Fri Jul 22, 2011 1:47 am
Area of Inner circle=pi*2^2=4Pi
Area Bigger Circle=pi*3^2=9Pi

Area of Ring = Area of Bigger Circle-Area of Inner Circle
=9pi-4pi=5pi

Area of Ring/Area of Inner Circle=5pi/4pi=5/4

9/4 would have been the answer if we were asked to find the ratio of the area of the bigger circle to the smaller circle.
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by Anurag@Gurome » Fri Jul 22, 2011 2:07 am
sampath wrote:If a ring is formed by the inner circle of radius 2 and the outer circle of radius
3, what is the ratio of the area of the ring to that of the inner circle?
Area of the inner circle = pi*(2)^2 = 4*pi
Area of the outer circle = pi*(3)^2 = 9*pi
Area of the ring = Area of the outer circle - Area of the inner circle = 5*pi


Hence, required ratio = (5*pi)/(4*pi) = 5/4
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