Sunday, May 12, 2013

2:32 PM

Probability


The probability of an event:

       0 = the event definitely won’t occur
       1 = the event definitely will occur
      0.5 = there is a 50/50 chance the event will occur

Probability that event A will happen:

The complement of an event:

The chance the event doesn’t occur--so the complement of drawing a green ball is drawing a ball that isn’t green.

P(event happens) + P(event does not happen) = 1


Mutually exclusive events:

Two events are mutually exclusive if they can’t happen together: P (A and B) = 0

Events A and B (if they are independent events):
                              P(A and B) = P(A) x P(B)
Events A or B:
                              A happens, B happens, or both A and B happen.

                              P (A or B) = P(A) + P(B) – P(A and B)

Events A and B (if A and B are dependent events):

                              P(A and B) = P(A) x P(B|A)
                              
                              P(B|A) is the probability that B occurs given that A occurs 
(example: the probability of drawing a heart, assuming you already drew a spade).
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