Puzzles/Logic puzzles/Getting out of Prison/Solution

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Puzzles | Logic puzzles | Getting out of Prison | Solution


"Out of the answers 'left' and 'right', which door would the other guard say doesn't lead to freedom, if I asked her?" - The answer will be the door that leads to freedom. Both guards will answer the same.

OR similarly

"Would the other guard tell me to go through your door to get to freedom?" If either guard says "Yes," go through the other guard's door. If either says "No," go through her door.. (Here actually a tautology[always true statement] is being asked from the guard. In simple form we are asking the question "Does freedom gate guard lie?")

OR alternatively

Trick question: "If I asked you whether the door you guard is the execution room, would you say yes?"

If the guard you asked was guarding the freedom room, the lying guard would have said Yes to the simple question "Is this the execution room?", but when asked whether he would say yes to this simple question, he has to lie and say No to the Trick question.

If the guard you asked was guarding the freedom room, the true guard would have said No to the simple question "Is this the execution room?", and when asked whether he would say yes to this simple question, he will truthfully say No to the Trick question.

Thus if it is the freedom door, either guard will give the answer No to the Trick question.

If the guard you asked was guarding the execution room, the lying guard would have said No to the simple question "Is this the execution room?", but when asked whether he would say yes to this simple question, he has to lie and say Yes to the Trick question.

If the guard you asked was guarding the freedom room, the true guard would have said Yes to the simple question "Is this the execution room?", and when asked whether he would say yes to this simple question, he will truthfully say Yes to the Trick question.

Thus if it is the execution door, either guard will give the answer Yes to the Trick question.

Therefore:

If the answer to the trick question by the guard you ask is No - then that guard is guarding the freedom door.

If the answer to the trick question by the guard you ask is Yes - then that guard is guarding the execution door.