This is a beautiful geometry puzzle contributed by my nephew, Karan Sharma. The puzzle originally appeared in a PSAT exam in 1980, and was not really a “puzzle” until one student proved that there was a different answer than what everyone had thought. Enough in already!
Here it goes – A tetrahedron and a pyramid with edges of unit length are glued together at one triangular face. How many exposed faces does the resulting solid have?
As always, please send your answers as comments within the blog (preferred), or send an e-mail to firstname.lastname@example.org. Please do share the puzzle with others if you like, and please also send puzzles that you have come across that you think I can share in this blog.
Happy geometry day!