Solving A Murder Case

Logic Level 2

One of X, Y, or Z has committed a murder! If only one of the statements is true, then who is the murderer?

Z Either X or Z X Y

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10 solutions

An easy way to find the murderer is analyzing statements 2 and 3. Both show the same result. So, both statements are either true or false. But as no two statements can be true, so both must be false so the Statement 1 (X's) is true and "Y" is the murderer.

Very intuitive

Rahul Agarwal - 5 years, 3 months ago

Not the way I solved it, since I didn't bother to notice identity of statements 2 and 3. Elegant!

Robert Schalit - 5 years, 4 months ago

Since one statement can be true though, as the directions say, why can't X's statement be true, and Y be the murdered? I am usually good at these, but this one threw me for a curve.

Nate Tucker - 5 years, 4 months ago

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X's statement is true. Y is the murderer. It got me too, the question wasnt which statement is true but which is the murderer. Y and z statements both say the same thing that z is the murderer. As we cany have two true statements that only leaves xs statement that y is the murderer. So i pressed x meaning i thought xs statement was true, and got it wrong as the question was who is the murderer...

Andrew Rakich - 5 years, 4 months ago

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Ah, I'm a dork. You're right, that's what I did wrong...

Nate Tucker - 5 years, 4 months ago

I did the same thing! I chose the true statement, instead of the murderer. Oops!

Lindsay Marie - 5 years, 3 months ago

I too have same doubt

vishwesh agrawal - 5 years, 4 months ago

Y is correct, your nomenclature is wrong though. Should have used numbering in answers I was right but got it wrong! Very ambiguous for math don't you think.

Randy Armstrong - 5 years, 4 months ago

shall we call Shinichi Kodo for this one?

edward refazo - 5 years, 3 months ago

This makes sense, ONLY ONE ANSWER IS CORRECT.

Joseph Toro - 5 years, 4 months ago

Nice logic dude......

Sayed M Amir - 5 years, 4 months ago

Suposing that the Z's statement is true and that Y and X's statement is false, Z is the murderer. But looking at Y's statement we can conclude that Z's statement is false. Suposing that the Y's statement is true and that X and Z's statement is false, Z is murderer. But looking at Z's statement we can conclude that Y's statement is false. Assuming that the X's statement is true and that Y and Z's statement is false, Y is murderer. Looking at other statement we can conclude that X's statement is true and Y is murderer.

I did the very same thing. Selected the true statement and not the murderer

Kirsteen Anderson - 5 years, 4 months ago
Sasidhar Naidu
Feb 12, 2016

1st consider "x " statement is true. After that "y" and "z". Make table between statements(columns) vs murderers(row)
For murderer X------F F F statements For murderer Y----- T F F
For murderer Z------F T T
Our condition is only one statement is true So "Y" is the murderer


Richik Sen
Feb 13, 2016

one statement not necessarily be true ; one situation has to be true(either x,y or z was the killer) both statement 2 and 3 point out that z is the killer since they both point out to a single situation,so i see no reason to dismiss statement 2 and 3

Ahsan Laghari
Feb 11, 2016

If statement of Y is true then the statement of Z is also true, but there only one statement gotta be True, Which the Statement of X !

Marvin Govindin
Jun 20, 2016

Am I the only one who found that X is saying the thruth because if he wanted to lie he could just have said that Z is the murderer, like that each statement is saying that Z is the murderer so it would be solved and Z would end up in jail. But no he is saying that it's Y so he is saying the truth. Is that logical ? Im not sure lol.

Viswa Gi
Feb 21, 2016

If what Z says is true, then Z is the murderer. But then what Y says must be false and Z cannot be the murderer. Therefore Z is telling false. Therefor Y is telling false and X the truth

Yousuf Kamal
Feb 12, 2016

Look at statements 2 and 3. Both indicates "Z" as murderer. So, both statements are either true or false. But as no two statements can be true, so they both must be false leaving beyond Statement 1 which is true. So Y is the murderer.

Arinjoy Basak
Feb 11, 2016

The problem can be solved using logic formulations as well (although I would like some feedback on this one): Consider: X - X committed the murder, Y- Y committed the murder, Z - Z committed the murder.

So, rule 1: Y Z ( X + Y ) Y\overline{Z}\overline({\overline{X+Y}}) \ rule 2: Y Z ( X + Y ) \overline{Y}Z(\overline{\overline{X+Y}}) \ rule 3: Y Z ( X + Y ) = Y Z ( X . Y ) \overline{Y}\overline{Z}(\overline{X+Y}) = \overline{Y}\overline{Z}(\overline{X}.\overline{Y}) \

Since only one of these is true, we can connect them by disjunction (OR)

rule 1 OR rule 2 OR rule 3 = Y Z X + Y + Y Z X + Y + Y Z ( X . Y ) Y\overline{Z}\overline{\overline{X+Y}} + \overline{Y}Z\overline{\overline{X+Y}} + \overline{Y}\overline{Z}(\overline{X}.\overline{Y}) = Y Z X + Y Z + Y Z X + Y . Z . X Y\overline{Z}X + Y\overline{Z} + \overline{Y}ZX + \overline{Y.Z.X} = Y Z Y\overline{Z} (by absorption of the first two terms) + Y ( X x n o r Y ) \overline{Y}(X xnor Y) (by distributive law on the last two terms, and considering the formula for xnor)

Now, either of these can be true, which means: i) Y committed the murder, Z did not. ii) or, Y did not commit the murder and either X and Z both committed it, or neither did.

Given the problem, we know that only one of them committed the murder, so it can't be both. So the second term is essentially useless.

Which means, Y committed the murder.

Well, that's what I figured anyway! Feedbacks?

Noa Galtung
Feb 11, 2016

If X and Y are both lying, then neither Y nor Z are the murderer, however, if Z is telling the truth then either X or Y is the murderer, so why can't X be the murderer? I can understand the logic for Y being the murderer but doesn't this work too?

If Z is telling the truth, neither X nor Y is the murderer. This is different than saying either x or y is the murderer. If Z is telling the truth, then Z would have to be the murderer. If that were the case, then Y would also be telling the truth. We can only have one person telling the truth though. Hope this helps.

Nate Tucker - 5 years, 4 months ago

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NICE EXPLAINATION BRO

Kumaresh Ghate - 5 years, 3 months ago

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