Thread: Problem 1.1
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Old 12-08-2015, 02:57 AM
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yaser yaser is offline
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Location: Pasadena, California, USA
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Default Re: Problem 1.1

Originally Posted by henry2015 View Post
Hi professor, with your example -- having two bags one with two black balls and one with two white balls.

I thought we had:
P[first ball is black] = P[B] = 1/2
P[first ball is black and second ball is back] = P[A and B] = 1/2
P[second ball is black given first ball is back] = P[A | B]
= P[A and B] / P[B] (by Bayes' Theorem)
= 1/2 / 1/2
= 1

eshmrt said "P[A|B]P[B] = 1/2" and you said the calculation is I am confused.

Maybe I miss something...
I can't see the discrepancy that is confusing you. "P[A|B]P[B] = 1/2" is correct because P[B]=1/2 and P[A|B]=1, both of which you correctly arrived at.
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