Several.
Several.
Whoops -- I had jumped directly from the subject line to the image, so I missed the six cubes.
These are side/top/bottom views of an object constructed by joining six identical cubes together. Also, I suspect that the five given views are not necessarily oriented in any way.
I think that a rectangle signifies two adjacent cubes located the same distance from the viewer. In other words, the faces of these two cubes form a rectangle because each face lies in the same plane. (There could be another cube behind the rectangle, in a view.) But a square next to a rectangle indicates that the face we see as the square lies at a different distance (closer or farther) than the cubes forming the rectangle.
Looking at #5, there are three cubes whose faces are at the same distance, and there are two other cubes whose faces are at a different distance. Where is the sixth cube? I think I can imagine its position, to render the other given viewpoints.
If I'm correct, the missing view will look like an L-shape, with a square attached to one of its longer sides. :cool:
The given pieces? You mean the 5 views? Those are 5 views of a single piece/object, which is formed by fusing several small cubes.
Take 2 cubes, put them on the floor side by side and look down. Imagine they fit together perfectly and there is no line in the middle. What shape do you see? A rectangle. Now add another "above" the left cube. You get an "L". Now put another cube on top of the one in the middle. The shape is still an "L", but now you see 2 lines - the edges of the last added cube.
The problem gives you 5 views of the object (for example: top, bottom, left, right, front) and asks you to deduce what it looks like from the back.
Hope it's clearer.