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.