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crackgmat007
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I have a feeling that this question has been answered before, but here goes:
You basically have two circles. The first one is the "white" circle, or the colored glass circle. We don't know the radius of this one, but you can easily find it out. The radius of the white circle will be the radius of the whole thing minus the width of the metal frame, i.e. r - s. This makes the surface of the white circle Pi*(r - s)^2.
The second circle is the medallion in itself. Its surface will of course be Pi*r^2.
So this means that the surface of the metal frame will be the surface of the medallion minus the surface of the white circle:
Pi*(r^2) - Pi*(r - s)^2 = Pi(r^2 - r^2 + 2rs - s^2) = Pi*(2rs - s^2) = Pi*s*(2r - s).
