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Help with this deduction? - Possibly for fans of Sherlock Holmes? watch

1. Here is the problem:
A detective is trying to figure out who murdered the victim. All the suspects make 3 statements, 2 of which are true and one is false. Who is the murderer?

Juan: I didn't kill him.
I've never possessed a knife.
It was Julian

Jose: I didn't kill him.
I don't have a knife
The others are often drunk

Jorge: I am innocent
Julian is the killer
I've never met Javier

Julian: I am innocent
Javier is the culprit
Juan lied when he said that I did it

Javier: I didn't kill him
Jose is the killer
Jorge and I are old friends

My thoughts are that the statements ''I've never met Javier'' and ''Jorge and I are old friends'' both can't be true,so one of them is false. However if, let's say ''Jorge and I are old friends'' is true, then Jorge is innocent and it was Julian. But, if Julian isn't innocent, then the statements ''it was Javier'' and ''Juan lied'' are true. So, that must mean that Javier's statement of ''Jorge and I are old friends'' must be false and therefore Jorge's statement of ''I've never met Javier'' is true.

Have any thoughts? Because I am just confused! haha
2. (Original post by Megsiie1)
Here is the problem:
A detective is trying to figure out who murdered the victim. All the suspects make 3 statements, 2 of which are true and one is false. Who is the murderer?

Juan: I didn't kill him.
I've never possessed a knife.
It was Julian

Jose: I didn't kill him.
I don't have a knife
The others are often drunk

Jorge: I am innocent
Julian is the killer
I've never met Javier

Julian: I am innocent
Javier is the culprit
Juan lied when he said that I did it

Javier: I didn't kill him
Jose is the killer
Jorge and I are old friends

My thoughts are that the statements ''I've never met Javier'' and ''Jorge and I are old friends'' both can't be true,so one of them is false. However if, let's say ''Jorge and I are old friends'' is true, then Jorge is innocent and it was Julian. But, if Julian isn't innocent, then the statements ''it was Javier'' and ''Juan lied'' are true. So, that must mean that Javier's statement of ''Jorge and I are old friends'' must be false and therefore Jorge's statement of ''I've never met Javier'' is true.

Have any thoughts? Because I am just confused! haha
All but one can be instantly eliminated by exactly the same thought process because if they lie about themselves they would have to be telling the truth in the other 2 statements
3. (Original post by Megsiie1)
Here is the problem:
A detective is trying to figure out who murdered the victim. All the suspects make 3 statements, 2 of which are true and one is false. Who is the murderer?

Juan: I didn't kill him.
I've never possessed a knife.
It was Julian

Jose: I didn't kill him.
I don't have a knife
The others are often drunk

Jorge: I am innocent
Julian is the killer
I've never met Javier

Julian: I am innocent
Javier is the culprit
Juan lied when he said that I did it

Javier: I didn't kill him
Jose is the killer
Jorge and I are old friends

My thoughts are that the statements ''I've never met Javier'' and ''Jorge and I are old friends'' both can't be true,so one of them is false. However if, let's say ''Jorge and I are old friends'' is true, then Jorge is innocent and it was Julian. But, if Julian isn't innocent, then the statements ''it was Javier'' and ''Juan lied'' are true. So, that must mean that Javier's statement of ''Jorge and I are old friends'' must be false and therefore Jorge's statement of ''I've never met Javier'' is true.

Have any thoughts? Because I am just confused! haha
You have deduced that "Jorge and I are old friends" is a lie. More concretely:
Suppose "Jorge and I are old friends" is true. Then Jorge's "I've never met Javier" is false, so Jorge's "Julian is the killer" is true. Hence Julian's "I am innocent" is false, so Julian's "Javier is the culprit" is true - but that's a contradiction (assuming only one person committed the murder).

Because you've identified Javier's lie, you know then that Javier's other two statements must be true. It remains to check whether it is consistent for Jose to be the killer (as Javier asserts truthfully), just to make sure that the problem is well-posed.
4. (Original post by Smaug123)
You have deduced that "Jorge and I are old friends" is a lie. More concretely:
Suppose "Jorge and I are old friends" is true. Then Jorge's "I've never met Javier" is false, so Jorge's "Julian is the killer" is true. Hence Julian's "I am innocent" is false, so Julian's "Javier is the culprit" is true - but that's a contradiction (assuming only one person committed the murder).

Because you've identified Javier's lie, you know then that Javier's other two statements must be true. It remains to check whether it is consistent for Jose to be the killer (as Javier asserts truthfully), just to make sure that the problem is well-posed.
Sooooooooo over complicated

Take juan ... If he is the killer then his first statement is a lie so his third statement must be true ... A contradiction

Everyone who accuses someone else can be eliminated by the same logic
5. (Original post by TenOfThem)
Sooooooooo over complicated

Take juan ... If he is the killer then his first statement is a lie so his third statement must be true ... A contradiction

Everyone who accuses someone else can be eliminated by the same logic
Over-complicated it may be, but it's what the OP had deduced
6. I got it! Anyone who claims to be innocent, and also claims someone else was the killer, cannot be the killer - because then they would have made two false statements. So Juan, Jorge, Julian and Javier must be innocent. Therefore Jose is the killer!

Thanks for the help anyways
7. (Original post by Megsiie1)
I got it! Anyone who claims to be innocent, and also claims someone else was the killer, cannot be the killer - because then they would have made two false statements. So Juan, Jorge, Julian and Javier must be innocent. Therefore Jose is the killer!
Exactly
8. (Original post by Megsiie1)
Here is the problem:
A detective is trying to figure out who murdered the victim. All the suspects make 3 statements, 2 of which are true and one is false. Who is the murderer?

Juan: I didn't kill him.
I've never possessed a knife.
It was Julian

Jose: I didn't kill him.
I don't have a knife
The others are often drunk

Jorge: I am innocent
Julian is the killer
I've never met Javier

Julian: I am innocent
Javier is the culprit
Juan lied when he said that I did it

Javier: I didn't kill him
Jose is the killer
Jorge and I are old friends
If we start with Julian, his first and last statements mean the same thing, making his second a lie.
That means it was not Javier.
Javiers' first is therefore true.
If we look at his third statement, the only way to cross-reference would be to look at Jorge's statements.
Jorge says that Julian is the killer, a fact that we have already dismissed. Therefore, Javier's final statement is false, making his second one true.
It was that **** Jose!

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