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CIRCLES

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Jinglander
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CIRCLES [#permalink] New post   31 Jul 2010, 14:46
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If the radius of a cirlce is triples what is the ratio of half the original circle area to area of the entire new circle



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Re: CIRCLES [#permalink] New post   31 Jul 2010, 16:32
What is 'triples' ??
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Re: CIRCLES [#permalink] New post   31 Jul 2010, 17:21
Triple

Posted from my mobile device
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Re: CIRCLES [#permalink] New post   31 Jul 2010, 22:56
1/36

Let the radious be 2R, half of radious is R and Tripple of the radiuls is 6R

Area of smaller circle = PI R^2

Are of bigger circle = PI (6R)^2 = PI * 36 R^2

Ratio = 1/36
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Re: CIRCLES [#permalink] New post   01 Aug 2010, 18:09
First post after lurking here a bit ^^
Givens: The old circle has radius R, and the new circle has radius 3R.
Looking for: (1/2*Area(Old circle))/(Area(New circle)) ->
(1/2)*pi*R^2/(pi(3R)^2) ->
(1/2)*pi*R^2/(9*pi*R^2)->
(1/2)/(9)->
1/18
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efet
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Re: CIRCLES [#permalink] New post   02 Aug 2010, 07:37
say r = 1
tripled circle will have pi*(3*1)^2 = 9pi
original circle pi*1^2 = pi

pi/2/9pi

1/18
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Re: CIRCLES [#permalink] New post   02 Aug 2010, 09:50
Fairly simple question. Area of a circle with respect to it's radius is \(/pi*r^2\) if radius is r. So now we have tripled the radius and we are taking half the original area.

New Circle Area \(= \pi*(3r)^2 = 9\pi*r^2\)
Half of Old Circle Area \(= \frac{\pi*r^2}{2}\)

Ratio: \(= \frac{\frac{\pi*r^2}{2}}{9\pi*r^2} = \frac{1}{18}\)
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Re: CIRCLES [#permalink] New post   02 Aug 2010, 13:30
amitjash wrote:
1/36

Let the radious be 2R, half of radious is R and Tripple of the radiuls is 6R

Area of smaller circle = PI R^2

Are of bigger circle = PI (6R)^2 = PI * 36 R^2

Ratio = 1/36



"Triple of radius is 3r, NOT 6R." Thus, the answer is 1/18.
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Re: CIRCLES [#permalink] New post   02 Aug 2010, 16:40
Jinglander wrote:
If the radius of a cirlce is triples what is the ratio of half the original circle area to area of the entire new circle


My reasoning

pi*r^2 is the frmula for the circle square. Let x be a factror.

so, x = pi*(3r^2)/pi(.5r)^2,

get rid of pi,

9r^2/.25r^2= 36



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Re: CIRCLES [#permalink]
02 Aug 2010, 16:40
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