Event (Probability)

Updated 09 Sep 2026

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Definition
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  an outcome, or a set of outcomes, of an experiment
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  formally: a subset $A$ of the universe (sample space) $U$ ; its probability is the sum of the weights of the elements in it, $\Pr[A] := \sum_{x \in A} P(x)$
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Note
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  the probability of the whole universe is 1 (since all weights sum to 1); the probability of any event lies in $[0, 1]$
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Example
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  over the universe of all 8-bit strings (256 of them), the event "the two least-significant bits are both 1" contains 64 strings, so under the uniform distribution its probability is $64/256 = 1/4$
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Related

Linked references 6