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If the diameter of circle R is 30% of the diameter of circle S, the ar

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Joined: 02 Sep 2009
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If the diameter of circle R is 30% of the diameter of circle S, the ar  [#permalink]

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26 Jan 2016, 01:51
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Difficulty:

25% (medium)

Question Stats:

87% (01:00) correct 13% (01:08) wrong based on 19 sessions

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If the diameter of circle R is 30% of the diameter of circle S, the area of circle R is what percent of the area of circle S?

A. 9%
B. 15%
C. 30%
D. 60%
E. 90%

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Re: If the diameter of circle R is 30% of the diameter of circle S, the ar  [#permalink]

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26 Jan 2016, 04:01
Let diameter of circle R , dr = 30
and diameter of circle S , ds = 100
Radius of circle R , Rr = 15
Radius of circle S , Rs = 50

Area of circle R/ Area of circle S = (pi * Rr ^2 ) /( pi * Rs^2 )
= (15/50)^2 = (3/10)^2
=9%
Alternatively , since diameters of the circle are in ratio 3:10
The area of circles will be in ratio 3^2 : 10^2
= 9:100
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Re: If the diameter of circle R is 30% of the diameter of circle S, the ar  [#permalink]

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26 Jan 2016, 04:04
Let diameter of S be 10m
Then, diameter of R will be 3 m
Now,
Area of S=pi(10)^2=100pi
Area of R=pi(3)^2=9 pi
Now,
x%of100pi=9pi
x=9%

Re: If the diameter of circle R is 30% of the diameter of circle S, the ar &nbs [#permalink] 26 Jan 2016, 04:04
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If the diameter of circle R is 30% of the diameter of circle S, the ar

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