The six faces of a three-inch wooden cube are each painted red. The cube is then cut into one-inch cubes along the lines shown in the diagram. How many of the one-inch cubes have red paint on at least two faces?
There are 3 x 3 x 3 = 27 one-inch cubes.
The center cube (which can't be seen from the outside) has no paint on it.
The six center cubes of the sides have only one sides painted.
All the rest have at least two sides painted.
27 - 1 - 6 = ...