A boy, a girl and a dog are standing together on a long, straight road. Simultaneously, they all start walking in the same direction: The boy at 4 mph, the girl at 3 mph, and the dog trots back and forth between them at 10 mph. Assume all reversals of direction instantaneous.
In one hour, where is the dog and in which direction is he facing?
(In reply to Official solution (spoiler)
Your link gives an interesting argument that, however, assumes that at some point the dog is between the boy and the girl. Reading the problem carefully, it seems quite possible that the dog will take off at ten miles an hour and keep going straight ahead for the hour and never be between the boy and the girl. The problem is not what I would call well-posed, in any event.
Posted by Richard
on 2004-01-24 12:25:45