Concrete delivered to a construction site costs $250 a cubic yard. What is the cost of the concrete needed to build a 6-inch-thick patio slab 20 feet by 10 feet?

Additional information:
The volume of a rectangular slab is the product of its three dimensions. The 6 inches thickness of the slab is 1/2 foot thick

Preliminary calculations
Compute the volume in cu ft for the entire job 20 (ft) * 10 (ft) * 1/2 (ft) = 100 (cu ft) Since this is the entire job
100 (cu ft /job)
Note: An alternative approach would be to include the volume calculation in
the equation below. However, doing it as a preliminary calculation seems more straight forward.

Let x equal what you are trying to find
x = ($ / job) Note: Made up unit "job" form above.
Reciprocal Factors
250 ($ / cu yd) 1 / 250 (cu yd / $)
27 (cu ft / cu yd) 1 / 27 (cu yd / cu ft)
Build an equation
x ($ / job) = 250 ($/cu yd) * 1 / 27 (cu yd / cu ft) * 100 (cu ft / job)
Multiply factors
x ($ / job) = 925.93 ($ / job) Cost of concrete is $925.93.