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Probability

Problem Solving — algebra and arithmetic (GMAT Focus Edition)
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Probability

by diegocuenca » Wed Jul 20, 2011 2:07 pm
I'm confused on the difference between these equations

Combined events: E and F = P(E and F) = P(E)P(F)

Conditional probability: the prob. of A and B occurring is the prob. of event A times the prob. of event B, given that A has already occurred.

P(A and B) = P(A) x P(B|A), is | supposed to mean B divided by A to account for A already occurring? If not what does it mean?

What is the difference between both of these equations?

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by vineeshp » Thu Jul 21, 2011 6:50 am
hi The | means probability of B given A.

Combined probability is what we apply all the time. Flipping coins twice. Probability of 2 heads is probability of first heads * probability of second heads.

Conditional probability is the case where Probability of the event B occuring is dependent on A occuring. Pulling balls out of a bag, one after the other? If there is a bag of 5 white and 6 red balls. What is the probability of withdrawing 2 whites?

Here the probability of getting white in first is 5/11
But the probability of geting white in second is 4/10. So probability of getting white in the second is dependent on getting a white in the first.
Vineesh,
Just telling you what I know and think. I am not the expert. :)
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by diegocuenca » Tue Jul 26, 2011 10:44 am
Awesome, that was a great explanation.
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