The seven pieces of cubes are named Soma cubes. Altogether you have 1x3 + 6x4 = 27 separate cubelets. The main problem of the Soma "research" is to assemble the seven Soma pieces or 27 cubelets to make a 3x3x3 cube. The chance of solving this three-dimensional puzzle is good, because there are 240 possibilities to put the cube together, not counting symmetries.