# Difference between revisions of "Expected value"

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The '''expected value''' or '''expectation''' is the (weighted) average of all the possible outcomes of an event, weighed by their [[probability]]. For example, when you roll a die, the expected value is (1+2+3+4+5+6)/6 = 3.5. | The '''expected value''' or '''expectation''' is the (weighted) average of all the possible outcomes of an event, weighed by their [[probability]]. For example, when you roll a die, the expected value is (1+2+3+4+5+6)/6 = 3.5. | ||

## Revision as of 03:20, 29 September 2009

The **expected value** or **expectation** is the (weighted) average of all the possible outcomes of an event, weighed by their probability. For example, when you roll a die, the expected value is (1+2+3+4+5+6)/6 = 3.5.

(Since a die doesn't even have a face that says 3.5, this illustrates that very often, the "expected value" isn't a value you actually expect.)