# Help anyone? ProbabilityWatch

#1
Attachment 697944been stuck on this a while ;/
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#2
(Original post by marinacalder)
Attachment 697944been stuck on this a while ;/
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1 year ago
#3
(Original post by marinacalder)
...
You have the following probabilities, letting where being the probability of choosing either a man, woman, someone who plays cricket, or someone who plays tennis.

and

You want to find .

Any thoughts/attempts?
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#4
(Original post by RDKGames)
You have the following probabilities, letting where being the probability of choosing either a man, woman, someone who plays cricket, or someone who plays tennis.

and

You want to find .

Any thoughts/attempts?
wait, so not P(woman intersect tennis)?
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1 year ago
#5
(Original post by marinacalder)
wait, so not P(woman intersect tennis)?
No because it's conditional probability.

You have and since you do not have . If the only sport was tennis, then yes you would have what you got there.
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#6
(Original post by RDKGames)
No because it's conditional probability.

You have and since you do not have . If the only sport was tennis, then yes you would have what you got there.

oh gosh, is there a way to really quickly work out whether it's conditional or not? I have trouble with this..
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1 year ago
#7
(Original post by marinacalder)
oh gosh, is there a way to really quickly work out whether it's conditional or not? I have trouble with this..
Yeah you just do it from the context... conditional is like saying 'OK here are two things (humans and sports, in this ex) that do not influence each other's probabilities of being chosen (ie if I pick a woman, I can still pick any sport I want that is available, whereas I cannot then pick a man)'

EDIT: Also the word 'given' is a trigger word for conditional probability in a question. i.e. 'What is the prob. of choosing event A GIVEN event B' - though this doesn't seem to be the case here. Then again, probability isn't really my thing.
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#8
(Original post by RDKGames)
No because it's conditional probability.

You have and since you do not have . If the only sport was tennis, then yes you would have what you got there.
Also, if it's conditional, does that mean that trying to work it out assuming there are 100 total members won't work? and if so , why is that?
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1 year ago
#9
(Original post by marinacalder)
Also, if it's conditional, does that mean that trying to work it out assuming there are 100 total members won't work? and if so , why is that?
What's the point in assuming the sample size? Probabilities here aren't influenced by this.
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#10
(Original post by RDKGames)
What's the point in assuming the sample size? Probabilities here aren't influenced by this.
Would you mind providing a solution to this?
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1 year ago
#11
2/5 are men who play cricket so 2/5 of 40% = 16%2/3 of the cricketing members are women - ie twice as many as the men , so 32%remaining men play tennis 3/5 of 40% =: 24%Which leaves 100- 16- 32- 24 = 28% women who play tennis ( or 7/25 )
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1 year ago
#12
(Original post by marinacalder)
Would you mind providing a solution to this?
I misinterpreted the info when it came to the probabilities I gave on conditionals, they should be and , and yes the question asks for after looking at it properly - sorry, been doing too many conditionals lately!

Then you know that

Then you know that

So then you have which you can solve for .

Then similarly get the probability for

Drawing up a table and doing this might be more intuitive.
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