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Solution to CyberTeaser B200
| Suppose one ant, in walking toward the other, tries to go toward the
barrier rather than around it (along the edges of the square). Certainly, its path should
be symmetric with respect to the barrier: if it follows two different paths, then one must
be shorter than the other, and the longer path wastes time. Also, when it gets to the base
of the barrier, the shortest way over is a path perpendicular to an edge that is not on
the ground. If we fold the barrier flat against the original square, we get the diagram at
the right. Since ABCD is a square, we are comparing a + b to c
+ d. Since a > c, the path along the edge of the original
square is the shortest. |
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