A conundrum by Russian puzzle maven Boris Kordemsky:
A work train composed of a locomotive and five cars has just stopped at a railway station when word comes that a passenger train is approaching. The smaller train must make way for it to pass through, but the station has only one siding, and this will accommodate only three cars (or an engine and two cars). How can it arrange to let the passenger train through?
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The work train backs into the siding and uncouples its three rearmost cars. Then it moves forward a sufficient distance. The passenger train passes entirely through the station, backs into the siding, and couples these three cars. Then it moves forward again into the main railway, backs entirely through the station, and uncouples the three cars. The work train backs into the siding, which will now accommodate it, and the passenger train can move forward on its way. Now the work train can emerge from the siding and recouple the three waiting cars.
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