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# semi circle ratio

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Manager
Joined: 01 Dec 2007
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05 Nov 2008, 20:53
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

explain ?
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semi circle f.jpg [ 69.15 KiB | Viewed 937 times ]

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Current Student
Joined: 28 Dec 2004
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Location: New York City
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05 Nov 2008, 22:11
I get 1/2

so the radius of the big circle is r, then white circle will have r=r/2

we have really 2 small white circles..

so pi*2*(r/2)^2 / pir^2=1/2

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SVP
Joined: 17 Jun 2008
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05 Nov 2008, 22:53
fresinha12 wrote:
I get 1/2

so the radius of the big circle is r, then white circle will have r=r/2

we have really 2 small white circles..

so pi*2*(r/2)^2 / pir^2=1/2

The question asks for the ration of white area to the shaded area. Hence, this will be 1/1.

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Intern
Joined: 31 Oct 2008
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06 Nov 2008, 00:25
total area: pi*RS^2/4
white region area: 4*pi*RS^2/16 * 1/2 (semicircles)
dark region area=total-white=pi*RS^2=pi*RS^2/8

ratio white/dark = 1

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Current Student
Joined: 28 Dec 2004
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06 Nov 2008, 08:26
I agree...damn what is it with my careless mistakes...grrr

how do i improve my focus????

scthakur wrote:
fresinha12 wrote:
I get 1/2

so the radius of the big circle is r, then white circle will have r=r/2

we have really 2 small white circles..

so pi*2*(r/2)^2 / pir^2=1/2

The question asks for the ration of white area to the shaded area. Hence, this will be 1/1.

Kudos [?]: 319 [0], given: 2

Intern
Joined: 04 Nov 2008
Posts: 15

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06 Nov 2008, 12:02
the solution is 1/1

the area of the white area = 2 circle with radius = 1/2 r
area ( White ) = 1/2 * ( r^2 * Pi )

Area of black = Area of the Big circle - Area of White area
Area of black = 1/2 * ( r^2 * Pi )

the ratio is clear 1/2

the solution is ( B )

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Re: semi circle ratio   [#permalink] 06 Nov 2008, 12:02
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