A regular tetrahedron has four equilateral triangles as faces. A regular square pyramid has four equilateral triangles and a square as faces. The faces of the tetrahedron are congruent to the triangular faces of the square pyramid.

A new polyhedron is created by gluing the tetrahedron and the square pyramid together at a triangular face so that the vertices of the triangles coincide. How many faces does this polyhedron have?

i'd say 7

a tetrahedron has 4 faces

a square pyramid has five

sticking two faces together takes them away.

so 4+5=9-2=7

Posted by daniel on 2004-12-18 01:10:18