one always lies riddle
one always lies riddle
Everyone loves to solve riddles and teasers. Recently, that’s what happened on the internet and social media. The nerds, geeks and just about everyone who loves a good riddle was forced to confront “one always lies riddle“. We are going to share it below and implore you to put on your thinking cap and come up with the correct answer.
Ever since this riddle “one always lies” appeared online, many have tried to answer it and only few have been able to get its answer right.
(Don’t worry, “one always lies riddle” answer is included.)
one always lies riddle
You are a prisoner in a room with 2 doors and 2 guards. One of the doors will guide you to freedom and behind the other is a hangman –you don’t know which is which.
One of the guards always tells the truth and the other always lies. You don’t know which one is the truth-teller or the liar either.
You have to choose and open one of these doors, but you can only ask a single question to one of the guards.
What do you ask so you can pick the door to freedom?
one always lies riddle answer :
The answer to one always lies riddle is:
If you asked the truth-guard, the truth-guard would tell you that the liar-guard would point to the door that leads to death.
If you asked the liar-guard, the liar-guard would tell you that the truth-guard would point to the door that leads to death.
Therefore, no matter who you ask, the guards tell you which door leads to death, and therefore you can pick the other door.
Comments of the one always lies riddle :
Choose a guard and ask him,
=> If you choose the truthful guard, he will give you an honest answer. Enter his door if he says “yes” and enter the other door otherwise.
=> If you choose the liar, he will lie about what his reply would be. Since that reply is also a lie, the two lies cancel out. Enter his door if he says “yes” and enter the other door otherwise.
Here is a twisted solution.
If you get the answer yes:
If the guard is a truthteller, the number of truths is odd, 1. is false, 2. is false, so 3. must be true.
If the guard is a liar, the number of truths is even, 1. is true, 2. is false, so 3. must be true.
If you get a negative answer:
If the guard is a truthteller, the number of truths is even, 1. is false, 2. is true, so 3. must be true.
If the guard is a liar, the number of truths is odd, 1. is true, 2. is true, so 3. must be true.
So regardless of the answer of the guard, the door you pointed at is the door to freedom, you can leave safely.
We’re going to be using a timing attack. Here’s how it works.
Ask one of the guards:
The truth-telling guard will be able to answer this right away. No matter how many nested self-referential clauses you put into that question, she doesn’t need to remember them or count them, and it always remains a trivial question to which she can always instantly give a truthful answer.
Thus, simply by checking whether the answer is instantaneous or not, you can tell whether the guard is a truth-teller or a liar (respectively), and therefore select a door according to the answer that the guard gave you, and whether that guard is the truth-teller or the liar.
My answer, assuming I ask one question only…
A. (if the Truth guard is asked) If the Truth guy is in front of DD, he answers NO. If not, he answers YES.
B. (if the Liar guard is asked) If the Liar is in front of DD, he answers NO. If not, he answers YES.
Either way, if we get a NO, then we’ve asked the guard in front of the death door, so we go to the opposite door. If we get a YES, then we’ve asked the guard not in front of the death door, so we go to the door behind them.
If we look at it from the other side, the possibilities are the following:
- The door is correct and the guard tells the truth: Then 1 is false, 3 is true, 2 depends on how the guide answers the whole (true if no, false if yes), which fits in both cases (011= no, 001 = yes) => the guard can answer in any way and will pick one answer.
- The door is correct and the guard lies: Then 1 is true, 3 is true, 2 is same as above, which in both cases is a lie (111=no=>yes, 101=yes=>no) => the guard can answer in any way and will pick one answer.
- The door is not correct and the guard tells the truth: Then 1 is false, 3 is false, 2 is same again, but this time it does not fit (010=yes >< 2 true, 000=no >< 2 false) => the guard cannot answer.
- The door is not correct and the guard lies: Then 1 is true, 3 is false, 2 is same again, but this time it’s the truth (110=no=>yes — 2 false, 100=yes=>no — 2 true) => the guard cannot answer.
Thus, the reasoning is: If the guard can answer then you pointed at the freedom door, if it cannot answer you pointed at the death door.
However, this has one big danger, similar to the Halting Problem: You have no idea whether the guard really cannot answer, or if it’s merely thinking about the decision yet what answer to pick, which may take quite a time! And additionally, every answer is assuming that if the guard answers, it answers as soon as it can. While for most answers this is not very relevant, for this answer a negation of this assumption would be fatal!
Leave a comment if you ACTUALLY got the correct solution before reading the complete article, or if you have an other answer for this riddle. And let us know if you’ve heard of any other great riddles!
Be sure to share this awesome riddle with your family and friends on social media to see if they can answer it.
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