Arectangle prism has length of 20 inches, a width of 2 inches and height of 3 1/4 inches. the prism is filled with cubes that have edge lengths of 1/4 inches. how many cubes are needed to fill the rectangle?

The first thing we must do is find the volume of the rectangular prism which will be given by:
 Vtotal = (20) * (2) * (3 1/4)
 Votal = 130 in ^ 3
 We now look for the volume of each individual cube:
 Vcube = (1/4) ^ 3
 Vcube = 1/64 in ^ 3
 The number of cubes will be:
 N = (Vtotal) / (Vcube)
 N = (130) / (1/64)
 N = 8320
 
 to fill the rectangle are needed 8320 cubes