Spotting the liar

Logic Level 1

Melinda and Bobarth make the following statements:

Melinda : Bobarth is lying.
Bobarth : Melinda is lying.

Who is lying?

Assumption: Each statement refers to the other's statement given above and not to any statement outside the scope of this problem.

Melinda Bobarth Both of them Neither one Can't tell

3 solutions

Geoff Pilling
Dec 27, 2016

In this case, either Melinda is lying, in which case Bobarth is telling the truth, or Bobarth is lying, which would imply that Melinda is telling the truth. Both would be consistent. Therefore, you $\boxed{\text{can't tell}}$ .

Where did you get the name Bobarth?

If our friend Bobarth were more devious and had said "Melinda is telling the truth" then there would be no consistent option/answer, not even "can't tell".

Brian Charlesworth - 4 years, 5 months ago

Haha... Yup!

Geoff Pilling - 4 years, 5 months ago

Sorry, but I need to disagree with this solution on temporal sequence grounds. Lying is a speech act, deliberately making (saying or writing) a false claim. When Melinda speaks, bobarth hasn't spoken yet, so she is deliberately incorrect to claim that he is lying (when in fact he hasn't said anything at all). Then when bobarth speaks, he is correct to call Melinda out for lying. The correct answer is that Melinda lied because she spoke first.

Scott Stonington - 4 years, 5 months ago

The time sequence isn't specifically stated, so they could be making their statements simultaneously, or Bobarth could have been the first to speak, which renders the answer "can't tell" all the more appropriate, (if also making the question itself less interesting). And if they did make their statements simultaneously, they could have agreed beforehand to say what they said just to mess with our heads. Or they just know each other to be two-bit liars and make such statements as a matter of course.

However, rather that getting the lawyers involved, I think that what Geoff was trying to create was a scenario that had two internally consistent but externally opposing outcomes. Perhaps if each made the statement "Whatever [other's name] says is a lie" would address your sequencing concerns.

Brian Charlesworth - 4 years, 5 months ago

It is definitely nice that you make problems that are (in terms of angles), acute to straight. :]

Razzi Masroor - 4 years, 5 months ago

I think answer would be both of them. firstly "Melinda" made a statement that 'bobarth is lying' means bobarth is really lying then "Bobarth" made a statement that 'Melinda is lying' means melinda really lying. both are pointing each other to get certain lair until someone stops making that statement but they maynot stop,then we could say both of them lying.

A Former Brilliant Member - 4 years, 5 months ago

I assumed the statements were made in the order they were written. (I am aware this was not thhe intended assumption, but I still got the correct answer.) As in, Melinda was telling us that whatever Bibarth was about to say was a lie. In which case, he is lying when he says she is lying, making her statement true and his false. Assuming she was lying, his statement is true, making hers false, which is tautological. So, you can't tell.

Logan Rozos - 4 years, 5 months ago

Mohammad Khaza
Jul 7, 2017

it's like a quarrel between brother-sister and parents don't know who is right.

Mark Toth
Jan 1, 2017

The answer to this question is very complicated. Yes, logic is required to answer this question; but not all logic works properly if it's one dimensional with no depth. Take this for example," The Adélie penguin is black and white. Old films are black and white. The Adélie penguin is the same as old films." We know this is not true, because it makes no sense. We need more information to find answer of the true liar(s). Such things would include knowing,"who started it, what's the background information, what are they lying about, what is their relationship, facial expression, etc..." In some cases, you cannot answer a question from paper alone; sometimes, you must experience it. You have to be a detective. The reason I think so many chose,"cannot tell," is because the problem is continuously progressing with no definite end. It is like a dividing by zero problem. This is why we cannot tell.

Spotting the liar

3 solutions

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