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Printsmc
counting and probability intermediate
Problem
Each edge of a cube is colored either red or black. Every face of the cube has at least one black edge. The smallest number possible of black edges is
(A)
(B)
(C)
(D)
Solution
Each black edge can only take care of two adjoining faces, so we know at least three will be needed. Once the first black edge is placed, it is easy to see that three will be sufficient, if they are separated and go in different directions: This gives the answer
Final answer
B