IMO Shortlist 1973 problem 13
Find the sphere of maximal radius that can be placed inside every tetrahedron that has all altitudes of length greater than or equal to
%V0
Find the sphere of maximal radius that can be placed inside every tetrahedron that has all altitudes of length greater than or equal to $1.$
Source: Međunarodna matematička olimpijada, shortlist 1973
Školjka 
