MathDB
We can fill in the three dimensional space - ILL 1990 NET4

Source:

September 18, 2010
geometry3D geometrytetrahedronoctahedronratiogeometry proposed

Problem Statement

Prove that we can fill in the three dimensional space with regular tetrahedrons and regular octahedrons, all of which have the same edge-lengths. Also find the ratio of the number of the regular tetrahedrons used and the number of the regular octahedrons used.