GMATPrep - area metal frame?

[California4jx]

I got this right - and its seems very straightforward, however, my answer was not coming right - I chose this because it was similar to what i was getting ... this is how I did it -- any thoughts ?

Area of metal frame = area of big ring - area of small ring

= PI (r+s)^2 - PI (r)^2
= PI { r^2 + s^2 + 2rs - r^2 }
= PI { s^2 + 2rs }
= PI*s (s + 2r)

There is no such answer ....

[nervesofsteel]

Medallion is made of circular glass+ metal ring..
and the radius is given for medallion

thus outer radius is given as r and thickness of metal ring is s

so the answer should be pi(r^2) - pi (r-s)^2

so the ans is E

[pepeprepa]

For the shaded region.
We calculate the total are less the white area.

pi*(r+s)² - pi*r² = pi * (r² + 2rs + s²) -pi*r² = pi*s*(2r + s)

Tell me where I am wrong

[rishi235]

@ pepeprepa

Why did u take pi*(r+s)???
It shud be pi*(r-s)

The area of the shaded portion is
Area of the entire circle - Area of the white portion

Now radius of the white portion = r-s & not r+s

So area of the shaded portion is
pi*r^2 - pi*(r-s)^

U'll get the ans as E

Hope u understood ur mistake...Lemme know if u still in doubt

[kuroneko1313]

r is the outer radius of the medallion, not the inside. r is the distance between the center of the medallion to its outer surface.

I did the same way as the thread started did too, thinking that r is the inside radius. The problem doesn't mention this very clearly imo.

[gmattester]

For the shaded region.
We calculate the total are less the white area.

pi*(r+s)² - pi*r² = pi * (r² + 2rs + s²) -pi*r² = pi*s*(2r + s)

Tell me where I am wrong

You are right. Even I have solved this problem in the same way and getting same answer. I am still not sure that I have understood this question in the right way becoz answers cannot be wrong