A large mound of gravel is piled in a shape of a cone. The circumference of the bottom of the pile is 250 feet. The height of the pile is 35 feet. How many cubic feet of gravel is in the pile?

The volume is given by
  v = (1/3)Bh
where B is the area of the base of the cone and h is the height of the cone.
The area of the base can be expressed in terms of the circumference (c) as
  B = (c^2)/(4π)

So, the volume is
  v = (1/3)(c^2/(4π))h
  = (c^2)*h/(12π)
  = (250 ft)^2*(35 ft)/(12π)
  ≈ 58,000 ft^3    (rounded to 2 significant figures)

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  ≈ 2100 yd^3