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27 Nov 2017, 23:33
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C
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Difficulty:
15%
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Question Stats:
76% (01:18) correct
24%
(01:50)
wrong
based on 103
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Two circles with radii r and r + 2 have areas that differ by 8π. What is the radius of the larger circle?
(A) 1
(B) 2
(C) 3
(D) 8
(E) 9
(A) 1
(B) 2
(C) 3
(D) 8
(E) 9
28 Nov 2017, 00:10
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C
Area of larger circle = pi.(r+2)^2
Area of smaller circle =pi.r^2
Difference is pi.((r+2)^2-r^2)=8.pi
Solving we get r=1. Hence radius of larger circle =3
Sent from my iPhone using GMAT Club Forum
Area of larger circle = pi.(r+2)^2
Area of smaller circle =pi.r^2
Difference is pi.((r+2)^2-r^2)=8.pi
Solving we get r=1. Hence radius of larger circle =3
Sent from my iPhone using GMAT Club Forum
28 Nov 2017, 15:08
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Bunuel
Two circles with radii r and (r + 2) have areas that differ by 8π:
\(π(r+2)^2 - (πr^2) = 8π\)
\(π(r^2 + 4r + 4) - πr^2 = 8π\)
\(πr^2 + 4πr + 4π - πr^2 = 8π\)
\(4πr + 4π = 8π\)
\(4πr = 4π\)
\(r = 1\)
Radius of larger circle = \((r + 2) = 3\)
Answer C
Check: Circle 1 area = \(π(1)^2 = π\). Circle 2 area = \(π(3)^2 = 9π\). Difference:\((9π-1π)=8π\)
