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Topic: Probabilities
Replies: 3   Last Post: Sep 5, 2012 7:08 PM

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Watch Watch this User
Posted: Mar 13, 2007 11:26 AM
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Hi all,

I've got the following phrase:


I would like to calculate the conditional probability P(B|A).
If I use a logical thought, I get:

P(B|A) = the_number_of_AB / the_number_of_A = 4 / 17 = 0.23

and if I use the formula P(B|A) = P(B inter A)/P(A) I get:
P(B inter A) = 4 / (23-1)
and P(A) = 17/23 then:

P(B|A) = 4/22 * 23/17 = 0.25

So I would like to know why the "logical thought" is wrong and if the
result is right with the formula.

Thanks a lot

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