S1 Probability Formulas

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  • Created by: Phoebe
  • Created on: 05-10-13 20:32

Addition Law

 =   P(A u B) = P(A) + P(B) - P(A n B)  

      OR

      P(A n B) = P(A) + P(B) - P(A u B)

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Conditional Probability

P(A n B) = P(A n B)

                  P(A)

P(A|B) = P(A n B)

               P(B)

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Multiplication Law

P(A n B) = P(B|A) x P(A)  

OR  

P(A n B) = P(A|B) x P(B)

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Mutually Exclusive

P(A or B) = P(A) + P(B)    

--   P(A n B) = 0

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Multiplication Law for INDEPENDENT EVENTS

P(A n B) = P(A) x P(B)

-> P(A|B) = P(A)

              = P(AnB)         = P(A)

                  P(B)

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Other Useful ones...

P(A) = P(A n B) + P(A n B')

P(A) = P(A|B) x P(B) + P(A|B') x P(B)

P(A u B) = P(A) + P(B) - P(A) x P(B) 

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Comments

? Secret - Team GR

thanks the formulas are helpful :)  but maybe give an example as this helps understand the formula even more

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