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Each of Benny, Denny, Kenny and Lenny either always lies or always tells the truth.

  • Benny claims that Denny is a liar.
  • Lenny claims that Benny is a liar.
  • Kenny claims that both Benny and Denny are liars.
  • Kenny also claims that Lenny is a liar.

Which of them always lies and which of them always tells the truth?

This puzzle came from a Leningrad Mathematical Olympiad.


1 Answer 1


Ok, so this is the key understanding that made this make sense.

Kenny says that both of Benny and Denny are liars. Because of Benny's statement that Denny is a liar, Benny and Denny will always have opposite truth values. If Benny is True then Denny is False and vise versa.

Which means

Kenny must be a liar. Which means he is lying when he says that Lenny is a liar. Thus Lenny is telling the truth when he says that Benny is a liar.

Thus the final outcome is

Lenny and Denny are the two truth tellers, and Kenny and Benny are the two liars.

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