# A four inch thick concrete slab i sbeing poured for a circular patio ten ft in diameter.?

A four inch thick concrete slab is being poured for a circular patio ten feet in diameter. Concrete costs $50 per cubic yard. Find the cost of the concrete, to the nearest cent. Help, my answer seems way off, thanks!

I got the same answer Rich so I guess I did it right, thanks!

10ft = 10/3 yards

4inch = 4/ thirty six yards

volume of concrete required = depth*pi*D^2 where D = diameter

pi * (4/36)*(10/3)*(10/3) = 100pi/81 = 3.879 cubic yards

cost = 3.879 * fifty =$193.925

Area of a circle = pi * r^2

r = d/2 = 10ft/2 = 5ft

A = pi * 5^2 = 78.54 ft^2

Volume = Area * depth

Vol = 78.54 ft^2 * 4in * 1ft/12in = 26.18 ft^3

1 yd^3 = twenty seven ft^3

$50/27ft^3 * 26.18ft^3 = $48.48

You have a cylinder, radius ten feet, height four inches = 4/12 feet = 1/3 feet

Volume = pi*r^2*h = 3.142 * ten * ten * (1/3) = 104.73 cu feet

1 cubic yard = 3*3*3 cubic feet = twenty seven cubic feet

So volume = 104.73/27 cubic yards = 3.9 cubic yards to one decimal place

You are using the diameter of the circle instead of the radius. The area of a circle is pi r squared, not pi d squared.