Men and (Were)Wolves

Logic Level 2

You are stuck in a room with 5 people. All you know is that at least one person among them is a werewolf. Humans tell the truth, while the werewolves will lie.

  • Alice : I am not a werewolf, but either Bob or Derrick is a werewolf.
  • Bob : Carol is a werewolf, and Erica is telling the truth.
  • Carol : Bob is a werewolf, and Derrick is telling the truth.
  • Derrick : Either Alice or Erica is a werewolf.

  • Erica : Everyone else is a werewolf.

  • Alice : 1

  • Bob : 2
  • Carol : 3
  • Derrick : 4
  • Erica : 5

Who is the werewolf? Phrase your answer as a number. For example, if all of them are werewolves, you would enter "12345". Go from smallest to largest.


The answer is 25.

Antimatter Bee by Antimatter Bee , 16, USA

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3 solutions

Richard Desper
Oct 26, 2020

Bob claims Erica is telling the truth. Erica says "Everyone else is a werewolf".
If Erica is telling the truth, Bob is a werewolf. If Erica is lying, Bob is also lying, and Bob is a werewolf. Either way, Bob is a werewolf.

Alice says "either Bob or Derrick is a werewolf". This is true. Alice is not a werewolf.

Erica can now be evaluated. Since Alice is not a werewolf, Erica is lying, and thus she is also a werewolf.

Derrick's statement is thus true, since he says "either Alice or Erica is a werewolf". Derrick is not a werewolf.

That leaves Carol, who truthfully says that Bob is a werewolf and that Derrick is telling the truth.

Summary: Alice, Carol, and Derrick are not werewolves while Bob and Erica are werewolves.

2 Helpful 1 Interesting 2 Brilliant 0 Confused
Antimatter Bee
Oct 26, 2020

When deducing the solution, I started with Erica. If Erica is telling the truth, then Alice is lying and is a werewolf, but then Derrick would be telling the truth, even though he is a werewolf. As a result, Erica must be lying to avoid this contradiction. If she is lying, then she is a werewolf and Derrick is still telling the truth. Thus, Derrick cannot be a werewolf. Since we know Derrick is telling the truth, then Carol is also telling the truth because she says that Derrick is telling the truth. Thus, Carol is not a werewolf. To add to this, Bob says Erica is telling the truth. Since we know that Erica is lying, then Bob is lying as well. With that in mind, Alice is correct in saying either Bob or Derrick is a werewolf, and she herself is not a werewolf. In conclusion, Bob and Erica are the werewolves.

1 Helpful 0 Interesting 1 Brilliant 0 Confused

This seems flawed:

"then Carol is also telling the truth because she says that Derrick is telling the truth. Thus, Bob is a werewolf."

Carol's statement is that Bob is a werewolf AND that Derrick is telling the truth. Knowing that Derrick is telling the truth isn't enough to resolve Carol's statement. And you cannot say Carol's statement must be true, thus Bob must be a werewolf. You need another path.

" To add to this, Bob says Erica is telling the truth. Since we know that Erica is lying, then Bob is lying as well."

Yes, because Bob says Erica is telling the truth, and you've already proven Erica isn't telling the truth, this forces Bob to be a werewolf. THEN you can conclude that Carol is telling the truth.

Richard Desper - 7 months, 2 weeks ago

The truth value for AND connective is 1 x 1 = 1. With only one 1 input at hand, it doesn't mean much since 1 x 0 = 0 x 1 = 0.

Saya Suka - 4 months ago
Saya Suka
Feb 8, 2021

Alice : I am not a werewolf, but either Bob or Derrick is a werewolf.
Bob : Carol is a werewolf, and Erica is telling the truth.
Carol : Bob is a werewolf, and Derrick is telling the truth.
Derrick : Either Alice or Erica is a werewolf.
Erica : Everyone else is a werewolf.



Reading over the conversation once, we should already have noticed the inconsistency in Bob's statement in which he supported Erica's that implicated everyone other than herself, including Bob the supporter, but it is a fact that truthful people are united by the same unity of truth principles, therefore we wouldn't ever find one truth teller getting accused by another truth teller. Also, in any case, Bob was either lying about Erica being a human (who really, actually is a werewolf) OR Erica told the truth about Bob being one of the 4 werewolves. With this, Bob is obviously a werewolf.

Let's look at Derrick's statement. The man could be another werewolf only if the women he mentioned were both humans, but Alice's and Erica's are not aligned with each other with one being defensive and one accusing the other. Thus, the two must be different creatures with opposing nature, making Derrick a human.

Werewolf Bob and human Derrick makes Carol another human with two truthful statements.

With at least two humans existing among the other 4, Erica is a werewolf and Alice, being opposite of Erica, is another human.

Werewolves : Bob & Erica
Answer : 25

0 Helpful 0 Interesting 0 Brilliant 0 Confused

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