Who Really Copied the Assignment?

[requied]

TL;DR Summary

someone is lying and there are statements. It's expected to find who copied the assignment.

If someone is lying, who copied the assignment?

Alex: Cate copied the assignment.

Cate: David copied the assignment.

David: Cate is lying.

Keil: I didn't copy.I think Cate is lying. If Alex is true and there is only one person who is lying, Cate and David can't be true at the same time. If other true guy is David, Cate is lying and Cate's thought is not true, so David did not copy the assignment. But already we can't know who copied. Please help

 

[Halc]

If other true guy is David, Cate is lying and Cate's thought is not true, so David did not copy the assignment.

If David is truthful, Cate's statement would indeed be false, which is consistent with David's statement. I'm not saying David is truthful or not, I'm saying your statement doesn't explain why.

You seem to be basing your conclusion on only statements Cate and David's comments. Try more.

 

[jedishrfu]

If you go with the assumption that everyone is telling the truth except for the plagiarist then I’d go with Cate.

The best method of solution though is to invite them all to a meeting with Patrick Jane of the CBI aka The Mentalist TV show and the plagiarist will be revealed.

 

[requied]

I think Patrick Jane also will reveal the plagiarist like me when he first saw the girl. So, you say Cate surely?

 

[Dale]

But already we can't know who copied.

Why not? If Cate is lying then Alex is not.

 

[jedishrfu]

This an example of Occams Razor where we know someone copied the work and they of course are hiding behind a lie. The others can be considered to tell the truth unless of course they are helping the plagiarist for reasons unknown. We seek the simplest explanation that answers the question and by Occam that is likely the correct one.

One other thing not considered for your problem is that in the real world some folks just don't know or will make false accusations from lack of knowledge or prejudice... One case awhile back was an guy was reported by a mother and daughter to the airport police for pouring some strange powder in his water. It turned out it was a cold remedy.

The Mentalist has a lot of great scenes where the offender is revealed leveraging certain knowledge of the case and surmising some additional conjectures and then testing them through absurdities or through misdirection of clues planted in the suspects minds to see how they'll react or what'll they do with it.

 

[hutchphd]

Nice puzzle. Just because someone is not telling the truth does not make it a lie! ( I could mention an example...but dare not). Only one liar here.

 

[AndreasC]

OK, is there only one liar or could there be more? If there is only one liar, then this is simple. David's statement can either be truth or lie. If it is true, then the one liar is Cate. Every other statement is true, so Alex is saying the truth and Cate is lying. If David's statement is a lie, then Cate is telling the truth. But if there is ONLY one liar, then Alex is also telling the truth, and that's a paradox because Cate and David can't both be at fault in the same time. Thus it is impossible for David to be the one liar.

However if there are more liars it's unsolvable.

 

[jedishrfu]

There may be some cases though where two liars are allowed or if all are liars but I think that's going beyond what the problem is designed for.

Some great stories result when there's a conspiracy of liars.