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Who committed the murder? (Posted on 2008-10-08) |
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Five criminals appeared before the court for sentence.
Their names,
strange to say, were Fraud, Libel, Blackmail, Theft and Murder - each
the namesake of the crime with which one of the others was charged.
The namesake of the crime with which Blackmail was charged was himself
charged with the crime of which the namesake was charged with murder.
The namesake of the crime with which Murder was charged was himself
charged with the crime of which the namesake was charged with fraud.
All the prisoners were found guilty and sentenced. Theft, for
example, got seven years. The criminal who was found guilty of murder was placed on death row.
Who committed the murder?
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Submitted by pcbouhid
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Rating: 3.0000 (1 votes)
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Solution:
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(Hide)
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Let x -> y to mean that x was charged with the crime y.
Of course, crimes and
criminals have the same names, so that x -> y -> z means that x was charged with the crime called y, and the criminal y was charged with the crime z.
Notice that x -> x is never true, as was stated in the problem. The next sentence of the
problem is a little hard to work out, but it ultimately comes down to B -> x -> y -> M and the sentence following is exactly parallel: M -> z -> w -> F.
Now, if we consider the five crimes/criminals, starting with, say, B, and looking at the sequence B -> x1 -> x2 -> x3 -> x4 -> ... we should find that the sequence repeats.
There are only five crimes (or five criminals) so some two x's will be the same. Then the sequence between them will repeat. Furthermore, since each
crime was only charged to one criminal, the sequence repeats backward to the B as well. This is a cycle, and the length of the cycle cannot be one, since no criminal was charged with his namesake.
That leaves two possibilities: a) Either two criminals were charged with one another's namesake (a cycle of length two) and the other three form a cycle of length three, or b) there is only one cycle of length five. (Of course, we can't have a cycle of length four, since the
leftover criminal would have to be charged with his namesake.)
But: B -> x -> y -> M and M -> z -> w -> F
means that B, M, and F cannot be in a cycle of length three. There are only two other criminals left, which isn't enough for a cycle of length three. That means that the first possibility is not possible, so there is only one cycle of length five.
So that means that we have B -> x -> y -> M -> z -> B with the cycle being (B, x, y, M, z).
But then M -> z -> w -> F
means that w = B, and F = x, so that our cycle is B -> F -> y -> M -> z -> B.
Now it only remains to determine y and z. We want to find out who was
charged with murder (and therefore convicted), which means who is y?
y was placed on death row, which means that y is not Theft, because Theft got seven years. So that means that z is Theft, and the
only remaining criminal is Libel, who must be the murderer y.
B -> F -> L -> M -> T -> B, and we conclude that:
Blackmail was charged with fraud, Fraud was charged with libel, Libel was charged with murder, Murder was charged with theft, and Theft was charged with blackmail.
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