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
_________________