Two ants are on opposite vertices of a regular octahedron (an 8-sized polyhedron with 6 vertices,
each of which is adjacent to 4 others), and make moves simultaneously and continuously until
they meet. At every move, each ant randomly chooses one of the four adjacent vertices to move
to. Eventually, they will meet either at a vertex (that is, at the completion of a move) or on an
edge (that is, in the middle of a move). Find the probability that they meet on an edge.
Answer: $\frac{2}{11}$