## Quick Reference

Four propositions about probabilities from which all major theorems can be derived: (1) the probability of any event is equal to or greater than zero; (2) the probability of a certain event is 1; (3) if *E* and *F* are two mutually exclusive events (events that cannot both occur), then the probability of the disjunction (the probabi-lity of either *E* or *F* occurring) is equal to the sum of their individual probabilities: *P*(*E* or *F*) = *P*(*E*) + *P*(*F*); and (4) the probability of a conjunction of two events *E* and *F* (the probability that both *E* and *F* occur) is equal to the probability of *E* assuming that *F* occurs multiplied by the probability of *F*: *P*(*E* and *F*) = *P*(*E* | *F*)*P*(*F*). [Named after the Russian mathematician Andrei Nikolaevich Kolmogorov (1903–87) who formulated them in 1933]

*Subjects:*
Psychology.

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