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Home > Logic > Liars and Knights
Knowing the Natives (Posted on 2003-08-16) Difficulty: 2 of 5
I met two natives on an island - Benny and Lenny. They are either a knight, a liar or a knave. Knights always tell the truth, liars always lie and knaves alternate between truth and lie. They tell me this:

Benny : We are both of the same type.
Lenny : I am a knave.
Benny : Lenny is a liar.

A knight then tells me what Lenny is. From this I was able to work out what they were.

What are Benny and Lenny?

See The Solution Submitted by Lewis    
Rating: 3.8000 (5 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Couple of Knaves | Comment 3 of 14 |
Most apparent is that Lenny's statement precludes him from being a knight, which in turn precludesBenny from being a knight by his first statement, so we're dealing with knaves and liars only. Assume Lenny is a liar, this means since Benny's second statement is true, he must be a knave and therefore his first statement would have to be true. However this yields a contradiction because Benny states he is of the same type as Lenny, a liar. Thus it must be that Lenny is a knave, which means Benny's second statement is false, if Benny were a liar then it would be a contradiction because his first statement would be true, therefore Benny is a knave also.
  Posted by Mr. Spock on 2003-08-16 11:30:54
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