Skip to main content
83 votes
Accepted

3 doors, three guards, one stone

No questions are required!
StephenTG's user avatar
  • 3,615
48 votes

Unfortunately, you died

Simple:
Ryan27's user avatar
  • 806
48 votes
Accepted

Liar liar pants on fire

I think the answer is: I mean,
Wen1now's user avatar
  • 9,253
47 votes
Accepted

Knights and Knaves: What does C say?

Jeff Zeitlin's user avatar
  • 4,274
47 votes
Accepted

Who robbed the store?

Two questions? The truth tellers that are not the criminal will simply answer "no". The liars that are not the criminal will know their answer would be "yes", so they also answer &...
Bass's user avatar
  • 77.6k
43 votes
Accepted

How many liars are in the room?

I am sure there are :
Jamal Senjaya's user avatar
43 votes
Accepted

The Second Hardest Logic Puzzle in the World

This solution works no matter what happens in the case of paradoxes or questions with ambiguous answers. First, ask: With this, A note: this problem is actually easier than it seems, because
Deusovi's user avatar
  • 147k
40 votes
Accepted

Who committed the crime?

Answer: Reasoning: And it fits the requirement of one truthful answer and one lie for each.
Marius's user avatar
  • 18.2k
40 votes
Accepted

Out of these 20 Doors, Which One Leads You to the Jackpot?

Plotting every answer's truth combinations would take a lot of room, so let's take a couple of shortcuts first: Assistant 2 is speaking the truth. There are no square numbers with 6 distinct divisors ...
Bass's user avatar
  • 77.6k
38 votes

The Knight never lies, the knave always lies, and the spy either lies or tells the truth

To start, A must be: Then, B must The means that C must
DqwertyC's user avatar
  • 8,216
37 votes

Batman vs 4 villains

This answer is kind of cheap and relies on some technicalities, but here goes: First round, ask everyone: Next, ask everyone: Now, we have one person we know is either always lying or always ...
DqwertyC's user avatar
  • 8,216
37 votes
Accepted

Ask one verbal question to figure out who is blind and who is mute among three persons

I think this could be an answer:
gustavovelascoh's user avatar
36 votes
Accepted

XKCD inspired logic puzzle

With two questions, you can ask for the first question: Based on the answer you'll know if they speak the truth or lies. If they're lying: If the they're telling the truth:
Siyual's user avatar
  • 1,347
36 votes

Who stole the flying car in Hogwarts?

This results
Oray's user avatar
  • 30.3k
33 votes

Batman vs 4 villains

The answer is The reason is This will also work if And just for kicks, However,
aleppke's user avatar
  • 579
33 votes

Knights and Knaves: What does C say?

A shortcut to get the correct answer, assuming that one exists, is to simply assume that A, B and C are all knights, and thus speak the truth. In this case, C will obviously answer "Yes." And since ...
Ilmari Karonen's user avatar
33 votes

The thief, liars, and the honest

Even simpler solution, with no hypotheticals needed:
Peter LeFanu Lumsdaine's user avatar
30 votes
Accepted

Find the identity of the four troll brothers

The mathematically minimum possible solution is: Credit to supercat and user1540815! I overlooked an important fact in my first draft. If the trolls stand in one line, there are 4 possible ...
Falco's user avatar
  • 2,201
30 votes
Accepted

Which day of the week is today?

Rewording their statements: Today is Monday. Today is Wednesday. Today is Tuesday. Today is not Monday, nor Tuesday or Wednesday. Today is Friday. Today is Wednesday. Today is not Sunday. We know ...
Rand al'Thor's user avatar
30 votes
Accepted

You trolls, get out of my party!

Solution: This was about the same thing I said before. But now... See Trenin's answer for a different formulation of the same approach, in case that one is easier to understand. Previous attempt at ...
Marius's user avatar
  • 18.2k
28 votes

Unfortunately, you died

Ask all you want...
user3294068's user avatar
  • 7,498
28 votes
Accepted

Knights and knaves in Landilandia

Ask the man that spoke to you: Reasoning: For the follow-up question: Reasoning behind this:
Levieux's user avatar
  • 10.5k
28 votes
Accepted

Robots in a spaceship

Answer Reasoning Furthermore
hexomino's user avatar
  • 136k
28 votes
Accepted

An Infinitude of Deceptive Devourers

Answer: Explanation: Consider two possible cases. Case 1 - the children used the "at least" convention: Let's consider two subcases. Case 1a - only a finite number of people ate cake Case ...
Joseph Sible-Reinstate Monica's user avatar
27 votes
Accepted

Batman vs 4 villains

At least half the time, Batman can get the order correct in only 4 questions. For certain sequences, it will take 5 questions. The Riddler's future answer would be "Yes", and since he answers ...
oobug's user avatar
  • 385
27 votes
Accepted

Which gnome is the tallest?

Jafe's user avatar
  • 77.5k
26 votes
Accepted

Three boxes, Four questions, Three times not true, Once the truth

JMP's user avatar
  • 35.6k
26 votes

How many liars are in the room?

This is the same answer as others have already found, but I would like to provide what I see as a better-worded explanation: (Note that the puzzle doesn't actually require knights who always tell the ...
Neremanth's user avatar
  • 632
25 votes

Unfortunately, you died

What if... Of course, then what follows is that...
Xenocacia's user avatar
  • 7,209

Only top scored, non community-wiki answers of a minimum length are eligible