Saturday, December 17, 2016

logical deduction - How many knights


In a room are 13 men, who are either Knights (truth tellers) or Knaves (lie tellers).


the first man looks around and says "The number of knights in this room is no greater than one"


the second man looks around and says "The number of knights in this room is no greater than two"


the third man looks around and says "The number of knights in this room is no greater than three"


and so on.


how many knights exactly are in the room?



Answer




There are 7 knights. The 7th knight is the first correct, and from 7-13 are 7 knights.


Every knight added eliminates a knave while increasing the threshold for truthiness. So, since one is increasing at the same rate that the other is decreasing, the result will end up near the middle.


If there are 6 knights, that would work down to knight 8, which would be untrue. If there are 8 knights, that would work down to knight 6, which is also untrue. 7 knights works down to knight 7.


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