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Blindfolded (Posted on 2003-12-30) Difficulty: 4 of 5
You are at one end of a hall blindfolded. At the other end are Alex and Bert. You are allowed to ask any yes or no questions you want, but only one of them will respond. They are standing next to each other and their voices are identical, so you have no way of telling which one responded by sound alone.

Using as few questions as possible, find out the type of each Alex and Bert and who answered your last question.

  Submitted by Brian Smith    
Rating: 4.3333 (6 votes)
Solution: (Hide)
Three questions are enough, but the questions asked depend on the previous responses.

This chart has five questions, but only three questions are used in a single application.

(Q1) Is the other person a knight?
If yes then goto (Q2a)
If no then goto (Q2b)

(Q2a) Does two plus three equal five?
If yes then both are knights, goto (Q3a)
If no then both are liars, goto (Q3a)

(Q2b) Would the other person say Alex is a liar?
If yes then Alex is a knight and Bert is a liar, goto (Q3b)
If no then Bert is a knight and Alex is a liar, goto (Q3b)

(Q3a) Would the other person say you are Alex?
If yes then Alex responded, stop
If no then Bert responded, stop

(Q3b) Would the other person say you are Alex?
If yes then Bert responded, stop
If no then Alex responded, stop

Comments: ( You must be logged in to post comments.)
  Subject Author Date
Hints/Tipsthe first questions is...axf2007-02-12 09:33:43
re(2): The answerkiara2005-03-21 22:32:39
Hints/TipsNo SubjectTyler2004-01-30 00:11:38
re: The answerles10212004-01-24 19:40:45
Solution5 questions or lessDave County2004-01-02 15:18:27
re(2): number of liars and knightsrerun1412003-12-31 14:51:16
re: number of liars and knightsdonnmike2003-12-31 01:59:17
The answerGamer2003-12-30 22:40:54
Solutionre: solution and proofPenny2003-12-30 21:26:51
Solutionsolution and proofTristan2003-12-30 19:58:03
Solutionre(2): number of liars and knightsrerun1412003-12-30 19:51:28
Some Thoughtsre: number of liars and knightsTristan2003-12-30 19:42:43
number of liars and knightsrerun1412003-12-30 18:48:01
the solutiondonnmike2003-12-30 18:28:56
re: another trydonnmike2003-12-30 17:58:51
re(3): another tryrerun1412003-12-30 17:46:28
re: another trydonnmike2003-12-30 17:44:33
re(2): another tryGamer2003-12-30 17:15:11
re: another tryPenny2003-12-30 15:32:41
another tryrerun1412003-12-30 15:03:16
One questionPenny2003-12-30 14:01:59
re: 2 questionsdonnmike2003-12-30 13:48:26
Solution2 questionsrerun1412003-12-30 13:30:20
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