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Day-knights and night-knights 3 (Posted on 2011-03-21) Difficulty: 3 of 5
Day-knights tell the truth in the day and lie at night. Night-knights lie in the day and tell the truth at night.
A:B is a day-knight.
B:A is a night-knight, and it is night.
What are A and B, and is it day or night?

  Submitted by Math Man    
Rating: 1.0000 (1 votes)
Solution: (Hide)
Suppose it is night. If A is a day-knight, then A is lying, so B is a night-knight. Then, B is telling the truth, so A is a night-knight. That is a contradiction. If A is a night-knight, then A is telling the truth, so B is really a day-knight. Then, B is lying, but A is a night-knight, and it is night. That is a paradox, so it is day. Therefore, B is lying, so B is a night-knight. That means that A is lying, so A is also a night-knight. Therefore, they are both night-knights, and it is day.

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  Subject Author Date
SolutionSolutionDej Mar2011-03-21 14:16:16
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