You are standing in front of two doors. One door leads to Heaven and the other leads to Hell. Each door is guarded by a gatekeeper. One gatekeeper always tells the truth, while the other always lies. You do not know which gatekeeper is truthful or which door leads where.
You are allowed to ask only one question to one of the gatekeepers.
What question should you ask to guarantee that you choose the door leading to Heaven?
Check if you were right - full answer with solution below.
Solution:
Step 1: Ask the question
- If I were to ask the other guard which door leads to Heaven, which door would he indicate?
Step 2: Understand the outcome
- If you ask the truthful guard, he will correctly tell you the answer given by the lying guard, which is incorrect.
- If you ask the lying guard, he will give a false version of the truthful guard’s correct answer, which again becomes incorrect.
Step 3: Key idea
- In both situations, the answer you receive will point to the wrong door (the door to Hell).
- Choose the opposite door to reach Heaven.