Geometry
posted by christy on .
A 4inchthick concrete slab is being poured for a circular patio 10 feet in diameter. Concrete costs $50 per cubic yard. Find the cost of the concerte, to the nearest cent. Show how you come to your answer.

1 cubic yard is 27 cubic feet. SO, concrete costs about $1.85 per cubic foot.
A 4" slab is 1/3 foot thick. So, the volume of concrete is the area of the patio, times its thickness, all in feet:
v = pi * 25 * 1/3 = 26.18 cubic feet.
cost = 26.18 * 1.85 = $48.43
Makes sense, since it's almost 1 cubic yard.