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imc

geometry intermediate

Problem

A rhombic dodecahedron is a solid with congruent rhombus faces. At every vertex, or edges meet, depending on the vertex. How many vertices have exactly edges meet?
(A)
(B)
(C)
(D)
Solution
Note Euler's formula where . There are faces. There are edges, because there are 12 faces each with four edges and each edge is shared by two faces. Now we know that there are vertices. Now note that the sum of the degrees of all the points is (the number of edges). Let the number of vertices with edges. Now we know . Solving this equation gives .
Final answer
D