A cubic object 3” x 3 “x 3” is painted blue
on all the outside surfaces, including the top and bottom. If the cube is cut
into 27 cubes of 1” x 1” x 1”, how many 1” cubes do have any painted surfaces?
Answer: only the box I in the very centre of the stack
will not suffer the storks of the brush, whereas all the other 26 boxes will
have at least one side painted.
