Wikipedia 10K Redux by Reagle from Starling archive. Bugs abound!!!

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Probability_Theory

:[[Probability]]
:[[Probability Axioms]] -- [[Probability Distributions]]

The basic theorems of probability can be developed easily from the [[Probability Axioms]] and [[Set Theory]]. 

#The sum of the probabilities for all the ''elementary events'' is one.
#For any arbitrary events, A1 and A2, the probability of both events, is given by the sum of the probabilities for all elementary events in both A1 and A2. If the intersection is empty, then the probability is exactly zero.
#For any arbitrary events, A1 and A2, the probability of either or both, , is given by the sum of the probabilities of the two events minus the probability of both.

*SUM Pr[Ei] = 1 
*Pr[A1*A2] = SUM of Pr[Ei] for all Ei in both A1 and A2. 
* Pr[A1+A2] = Pr[A1] + Pr[A2] - Pr[A1*A2]

The probability of some event happening knowning that some other one happened before can be computed using [[Conditional Probability]].
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[[Dick Beldin]]