Few people know there is an asylum in the land of Knights and Liars. The asylum houses mental deviants called 'Patients' who randomly tell the truth or lie.

Its visiting day and Frank has just started the evening shift. There is only one group of visitors left. Unfortuneately, the previous guard forgot to tell Frank which one of the five people seated at the table is the Patient. (There is exactly one Patient at the table. There are no Knaves.) Frank asks the group "Which one of you is the Patient here?" He got the following responses:

Alex:Bert is the Patient.
Bert:Carl is not the Patient.
Carl:I am not the Patient.
Dave:I am not the Patient.
Eddy:Dave is the Patient.

This left Frank puzzled, so he asks "Who amongst you can I believe?" This time the responses were:

Bert:Carl is a 'Knight'.
Carl:Dave is a 'Liar'.
Dave:Alex is a 'Liar'.
Eddy:I am a 'Knight'.
Alex did not say anything this time.

Wanting to get a straight answer, Frank decides he should pull one member of the group aside to ask one last question.

Who should Frank choose and what question should he ask?

NOTE: If Mr X is the Patient, then the statements "Mr X is a 'Knight'" and "Mr X is a 'Liar'" are both false.

Answer: He should choose Dave, who is the only Knight, and ask him any question. Dave will give him a straight answer. 

Since there is exactly one Patient, and everybody else is either a Knight or a Liar, there can't be more than one person telling a mixture of truths and lies. The only arrangement that allows this is:

 

Posted by Penny on 2004-10-27 18:14:32