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

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riderofgiraffes

Posts: 408
From: UK
Registered: 1/11/07
Re: Probabilities
Posted: Mar 13, 2007 11:56 AM
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Anonymous wrote:

> I've got ... BABAAAAAABAAABBAAAAAABA
>
> I would like to calculate the conditional
> probability P(B|A).


> If I use a logical thought,

Excellent - someone who is thinking about what's
actually happening, and not just blindly using a
formula.

> ... 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:


Should you really be using all 23 possible places
for the "A"?

> 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.


You need to worry about the edge cases.



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