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Math Expert V
Joined: 02 Sep 2009
Posts: 55630
A racetrack bounded by two concentric circles, one with a diameter of  [#permalink]

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Difficulty:   65% (hard)

Question Stats: 54% (02:00) correct 46% (02:29) wrong based on 81 sessions

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A racetrack bounded by two concentric circles, one with a diameter of 160 yards and the other with a diameter of 140 yards, is to covered with asphalt. If the asphalt layer is to be 1 foot deep, how many cubic yards of asphalt will be needed? (1 yard = 3 feer)

(A) $$75\pi$$

(B) $$90\pi$$

(C) $$500\pi$$

(D) $$1500\pi$$

(E) $$2000\pi$$

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examPAL Representative P
Joined: 07 Dec 2017
Posts: 1072
Re: A racetrack bounded by two concentric circles, one with a diameter of  [#permalink]

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Bunuel wrote:
A racetrack bounded by two concentric circles, one with a diameter of 160 yards and the other with a diameter of 140 yards, is to covered with asphalt. If the asphalt layer is to be 1 foot deep, how many cubic yards of asphalt will be needed?

(A) $$75\pi$$

(B) $$90\pi$$

(C) $$500\pi$$

(D) $$1500\pi$$

(E) $$2000\pi$$

Since the calculation required is straightforward, we'll just do it.
This is a Precise approach.

We need to calculate the area between the two circles and multiply it by a height of 1 foot = 1/3 yard.
This is $$\pi *80^2 - \pi*70^2 = 6400 \pi - 4900 \pi = 1500 \pi$$.

(C), 1500/3 = 500 is our answer
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Intern  B
Joined: 12 Feb 2018
Posts: 9
Re: A racetrack bounded by two concentric circles, one with a diameter of  [#permalink]

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1
Bunuel please edit the question if you have time. This kind of question in gmat provides always the convesion between the units feet- yards
Math Expert V
Joined: 02 Sep 2009
Posts: 55630
Re: A racetrack bounded by two concentric circles, one with a diameter of  [#permalink]

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Mikimix wrote:
Bunuel please edit the question if you have time. This kind of question in gmat provides always the convesion between the units feet- yards

Done. Thank you.

Check other Conversion problems to practice in Special Questions Directory.
_________________ Re: A racetrack bounded by two concentric circles, one with a diameter of   [#permalink] 05 Mar 2018, 07:17
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