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Probability is the chanse of something happening.

Ex 1: The Probability of getting a 3 on a 6-dice is 1/6.

Ex 2: The probablity of of raining in Sahara Desert is very low.


In mathematics there are four basic rules:

  1. For any event A, 0 ≤ P(A) ≤ 1.
  2. P(impossible event) = 0. Also written P(empty set) = 0 or P() = 0.
  3. P(sure event) = 1. Also written P(S) = 1, where S is the sample space.
  4. P(not A) = 1 – P(A). Also written P(complement of A) = 1 – P(A) or P(A^C) = 1 – P(A) or P(Â) = 1 - P(A)

If all outcomes of an experiment are equally likely, then:

P(A) = number of outcomes in event A / number of outcomes in the sample space