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m12 34

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Intern
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Joined: 07 Oct 2011
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m12 34 [#permalink] New post 11 Jun 2012, 17:25
If the diameter of a compact disk is 14 cm and the diameter of the hole in the center of the disk is 2 cm, what is the area of the compact disk?

1) 48pi
2) 52pi
3) 76pi
4) 122pi
5) 140pi

Could someone please explain clearly, if possible with diagram?
Intern
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Joined: 10 Mar 2012
Posts: 28
Location: India
Concentration: International Business, Strategy
Schools: INSEAD Jan '15
GMAT Date: 11-30-2012
WE: Design (Manufacturing)
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Re: m12 34 [#permalink] New post 11 Jun 2012, 19:38
karthiksms wrote:
If the diameter of a compact disk is 14 cm and the diameter of the hole in the center of the disk is 2 cm, what is the area of the compact disk?

1) 48pi
2) 52pi
3) 76pi
4) 122pi
5) 140pi

Could someone please explain clearly, if possible with diagram?


Area of the compact disc would be the difference between the area of the disc minus the area of the hole:

Compact Disc:
Dia = 14cm / radius = 7cm
Area = Pi*7^2=49Pi

Hole:
Dia = 2cm/radius = 1cm
Area = Pi*1^2=Pi

Hence area of the compact disc = 49Pi-Pi=48 Pi
Answer choice A
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Re: m12 34 [#permalink] New post 11 Jun 2012, 21:51
Buy a donut, there's your diagram. The donut's big loop has radius of 7, hole has radius of 1
So if you want to know the area covered by the donut itself is

7*7*pi - 1*1*pi = 48 pi

http://www.millersamuel.com/files/2012/ ... ddonut.jpg
Re: m12 34   [#permalink] 11 Jun 2012, 21:51
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