Conditional Probability
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Conditional Probability

[From: ] [author: ] [Date: 12-11-29] [Hit: ]
org/Regents/math/… which may help.Heres how I look at conditional probabilities.You have this universe of events that may take place, with known probabilities.A conditional probability looks at some subset of those, and examines the probability within that subset.......
Does any one have "worked problems" or sample problems with answers in pdf for Conditional Probability , I really don't understand this concept ?

Thanks

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Did you search the web? I easily found http://www.regentsprep.org/Regents/math/… which may help.

Here's how I look at conditional probabilities. You have this universe of events that may take place, with known probabilities. A conditional probability looks at some subset of those, and examines the probability within that subset.

E.g., the probability of rolling two dice and getting a nine is 4/36 = 1/9
That's because there are only 4 ways to get a 9: 36 63 45 54, out of 36 total ways to roll two dice.

Now let's restrict the situation. What's the probability of rolling a 9, given that one of the dice is a 3. Now we don't have the whole universe of 36 possilble rolls. We only have 11:
31 32 33 34 35 36 13 23 43 53 63. Only 2 are 9's: 36 63. So the conditional probability, "rolling a 9 given that one of the dice is a 3" is 2/9.

The formula for conditional probability just cut things down to these numbers. The formula would say that this = Pr(9 and a 3) / Pr(3).
Pr(total=9 and one die = 3) = 2/36 since there are 2 ways to do this out of the 36 total.
Pr(one die = 3) = 11/36
And again the conditional probability is 2/36 / 11/36 = 2/11.

Hope this helps. Your idea to get some practice is an excellent one. That's the best way to learn this well.
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