Difference between revisions of "Some Probability Formulas"
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[[File:Addition_Rule_Formula.JPG]] | [[File:Addition_Rule_Formula.JPG]] | ||
| − | We subtract the probability of both ''A'' and ''B'' occurring, as to not "double count" them. This can seen better by looking at the following Venn Diagram: | + | We subtract the probability of both ''A'' and ''B'' occurring, as to not "double count" them. This can be seen better by looking at the following Venn Diagram: |
[[File:A_and_B_Venn_Diagram.JPG]] | [[File:A_and_B_Venn_Diagram.JPG]] | ||
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'''Conditional Probability''' | '''Conditional Probability''' | ||
| − | Sometimes we would like to know the probability of an event ''B'' occurring, given that another event ''A'' has already occurred. This | + | Sometimes we would like to know the probability of an event ''B'' occurring, given that another event ''A'' has already occurred. This is called conditional probability and we use the notation: |
[[File:Condition_Probability_Notation.JPG]] | [[File:Condition_Probability_Notation.JPG]] | ||
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[[File:Conditional_Probability_Formula.JPG]] | [[File:Conditional_Probability_Formula.JPG]] | ||
| − | '' | + | ''contributed by David Ciskowski'' |
| + | ''edited by Paula Connolly'' | ||
Latest revision as of 13:45, 24 November 2025
Some useful probability formulas
The Addition Rule
Consider 2 events, A and B. To find the probability that either A or B (or both) will occur, we can use the following formula, called the addition rule:
We subtract the probability of both A and B occurring, as to not "double count" them. This can be seen better by looking at the following Venn Diagram:
Conditional Probability
Sometimes we would like to know the probability of an event B occurring, given that another event A has already occurred. This is called conditional probability and we use the notation:
This is read as "The probability of B given A," and can be calculated as follows:
contributed by David Ciskowski edited by Paula Connolly
