Wafer in a Box
Ralph Alexander, John E. Wetzel · Mathematics Magazine · 2005
An answer would provide a necessary and sufficient condition on the positive reals a, b, c, and p for a disk of radius p to fit in an a x b x c box, in the spirit of Post's 1993 necessary and sufficient condition on the six sides for one triangle to fit into another [8]. Our argument makes use of the penny in a corner problem from the 1948 William Lowell Putnam Mathematical Competition [9], for which we give a simple solution.