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# In the formula above

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In the formula above [#permalink]  29 Dec 2016, 09:28
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Question Stats:

83% (00:49) correct 16% (00:54) wrong based on 6 sessions
$$A=\frac{\pi*d^2}{x}$$

If the formula above gives the area A of a circular region in terms of its diameter d, then x=

(A) $$\frac{1}{4}$$

(B) $$\frac{1}{2}$$

(C) 1

(D) 2

(E) 4
[Reveal] Spoiler: OA

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Re: In the formula above [#permalink]  29 Sep 2017, 07:03
The formula for a circular region is $$A=\pi*r^2$$. The one given has the diameter instead of the radius, but since we know that d = 2r, we can write

$$\pi*r^2 = \frac{\pi*(2r)^2}{x}$$, where d = 2r, then

$$\pi*r^2 = \frac{\pi*4r^2}{x}$$.

Thus, in order for the two formulas to be equal, x = 4. Answer E!
Re: In the formula above   [#permalink] 29 Sep 2017, 07:03
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