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=92=7

Posted by daniel
on 20041218 01:10:18 