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Multiplication Rule

Multiplication Rule

A method for finding the probability that both of two events occur.

 

Multiplication Rule: If A and B are independent, P(A and B)=P(A)P(B). Otherwise, P(A and B)=P(A)P(B|A).


Example: P(rolling 1 on both rolls) = P(A and B) = P(A)P(B) = 1/6 · 1/6 = 1/36
Example using Multiplication Rule: bag with 3 red, 3 black balls. P(A)=1/2, P(B|A)=2/5, P(A and B)=1/5.

 

See also

Independent events, addition rule, conditional probability