Please help me with probability question. :(
I'm really confused by this question, I understood the others but is this just adding or do I multiply the probabilities? Multiplying gives a much lower number (0.2 * 0.6 = 0.12) and surely uncovering new evidence makes it more likely he's guilty? Do I multiply by a different number? Is it 0.8 * 0.6 because if 20% of the population has the characteristic then you can be 80% sure? That sounds wrong, I have a feeling I'm missing something.
Can you please explain this?
Thank you so much if anyone can, it's really appreciated.
Anyone?
Have to say, I failed to get it, so I await developments with interest.
It's almost certainly Bayes' theorem that's required, but I'm clearly not looking at it correctly.
It's almost certainly Bayes' theorem that's required, but I'm clearly not looking at it correctly.
(edited 9 years ago)
Original post by ghostwalker
Have to say, I failed to get it, so I await developments with interest.
It's almost certainly Bayes' theorem that's required, but I'm clearly not looking at it correctly.
It's almost certainly Bayes' theorem that's required, but I'm clearly not looking at it correctly.
I was thinking Bayes' theorem too, but I don't think we have enough information?
Original post by Financechick
I'm really confused by this question, I understood the others but is this just adding or do I multiply the probabilities? Multiplying gives a much lower number (0.2 * 0.6 = 0.12) and surely uncovering new evidence makes it more likely he's guilty? Do I multiply by a different number? Is it 0.8 * 0.6 because if 20% of the population has the characteristic then you can be 80% sure? That sounds wrong, I have a feeling I'm missing something.
Can you please explain this?
Thank you so much if anyone can, it's really appreciated.
I'm really confused by this question, I understood the others but is this just adding or do I multiply the probabilities? Multiplying gives a much lower number (0.2 * 0.6 = 0.12) and surely uncovering new evidence makes it more likely he's guilty? Do I multiply by a different number? Is it 0.8 * 0.6 because if 20% of the population has the characteristic then you can be 80% sure? That sounds wrong, I have a feeling I'm missing something.
Can you please explain this?
Thank you so much if anyone can, it's really appreciated.
Is there a mark scheme or any numerical answer given for this?
Original post by ghostwalker
Have to say, I failed to get it, so I await developments with interest.
It's almost certainly Bayes' theorem that's required, but I'm clearly not looking at it correctly.
It's almost certainly Bayes' theorem that's required, but I'm clearly not looking at it correctly.
I'm not at all sure either. But then I tend to find most probability questions seem to be written by Satan himself (overly wordy, liable to half a dozen different interpretations, counter-intuitive, etc)
I guess that it's looking for some kind of conditional probability argument, but I'm not sure how to deal with the Inspector's estimation of guilt of 60%. Does this mean that the suspect belongs to a population 60% of whom committed a similar crime, or what?
Original post by rayquaza17
I was thinking Bayes' theorem too, but I don't think we have enough information?
Is there a mark scheme or any numerical answer given for this?
Is there a mark scheme or any numerical answer given for this?
Apparently its departmental policy not to provide answers to past papers
Original post by atsruser
I'm not at all sure either. But then I tend to find most probability questions seem to be written by Satan himself (overly wordy, liable to half a dozen different interpretations, counter-intuitive, etc)
I guess that it's looking for some kind of conditional probability argument, but I'm not sure how to deal with the Inspector's estimation of guilt of 60%. Does this mean that the suspect belongs to a population 60% of whom committed a similar crime, or what?
I guess that it's looking for some kind of conditional probability argument, but I'm not sure how to deal with the Inspector's estimation of guilt of 60%. Does this mean that the suspect belongs to a population 60% of whom committed a similar crime, or what?
I think we'e to take the suspect's probability of guilt as 60% initially and that we've to work out how the suspect belonging to the 20% of the population with that characteristic affects the percentage probability of his guilt.
Original post by Financechick
I'm really confused by this question, I understood the others but is this just adding or do I multiply the probabilities? Multiplying gives a much lower number (0.2 * 0.6 = 0.12) and surely uncovering new evidence makes it more likely he's guilty? Do I multiply by a different number? Is it 0.8 * 0.6 because if 20% of the population has the characteristic then you can be 80% sure? That sounds wrong, I have a feeling I'm missing something.
Can you please explain this?
Thank you so much if anyone can, it's really appreciated.
I'm really confused by this question, I understood the others but is this just adding or do I multiply the probabilities? Multiplying gives a much lower number (0.2 * 0.6 = 0.12) and surely uncovering new evidence makes it more likely he's guilty? Do I multiply by a different number? Is it 0.8 * 0.6 because if 20% of the population has the characteristic then you can be 80% sure? That sounds wrong, I have a feeling I'm missing something.
Can you please explain this?
Thank you so much if anyone can, it's really appreciated.
I'm lousy at prob at the best of times but this looks like some sort of variant of Bayes' theorem.
If you google Bayes theorem and read the 1st paragraph of the Wikipedia article (the one about the train conversation) is it possible to re-word the question you've got in the same sort of language?
Original post by Financechick
Apparently its departmental policy not to provide answers to past papers
Can you not email your lecturer and ask for help?
I was thinking of using Bayes' theorem with the theorem of total probability, but I can't get it to work. :/
Original post by Financechick
...
Original post by rayquaza17
...
Original post by atsruser
...
Found on the 'net.
Original post by ghostwalker
Found on the 'net.
Hi, thanks so much!
where did you find that?
our past papers aren't meant to be public...
Original post by Financechick
Hi, thanks so much!
where did you find that?
our past papers aren't meant to be public...
where did you find that?
our past papers aren't meant to be public...
It's in a book. Don't know which came first.
Just google the phrase highlighted in yellow in jpeg, put it in quotes.
A First Course in Probability by Sheldon Ross, 8th edition.
(edited 9 years ago)
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