what is the largest number of regions the planes divide the space into? What's the smallest?

Question

Visualize 4 planes in space. Assuming that none of the planes lie exactly together, what is the largest number of regions the planes divide the space into? What's the smallest? Use pictures to demonstrate. 

Answer 1

The smallest is 5. Just take 4 parallel planes.

 

The largest is 15. Take the planes containing the faces of any tetrahedron.

 

 

Note: Statistically, if you choose 4 planes at random, they will almost surely divide the space into 15 parts.