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December 13th, 2012, 03:02 PM   #1
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Formulation of a Question - Probability

Hello, I'm new in this forum
I'm not a native English speaker, so I apologize for any mistakes in advance.

This problem was in my Mathematics test:
Quote:
A ship has disappeared in the ocean. We admit that the situation has been caused by any of the following equiprobable causes:
sinking
sequestration
destruction by storm

To each case, the probability of the rescuing team manages to rescue all the crewmembers alive is, respectively, 4/5, 3/5 and 7/10

[1st question - Calculate the probability of all crewmembers with life being saved.]
2nd question - We now know that 14 crewmembers were saved and that the cause of the disappearance was not the storm. After all, how many crewmembers were in the aforesaid ship?
My teacher says the answer for the 2nd question is 30.
I say the question makes absolutely no sense, as all we know are the odds (conditioned for each cause) for all of the crewmembers to survive. 14/30 would be the propotion between the number of rescues with all people saved and the total number of rescues.
I tried to explain my view to her, but she says she doesn't understand my problem with this question... Am I crazy or is she the one who seriously needs holidays?
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December 14th, 2012, 01:35 PM   #2
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Re: Formulation of a Question - Probability

Quote:
To each case, the probability of the rescuing team manages to rescue all the crewmembers alive is, respectively, 4/5, 3/5 and 7/10
The teacher seems to interpret that statement to mean the probability that a given person is rescued is the number stated.

As stated the problem is insoluble.
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