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Introduction to Probability. Approaches to probability. The classical approach The relative frequency approach The subjective approach. Mutually exclusive events. Two events are mutually exclusive (or disjoint ) if the occurrence of one of the events precludes the simultaneous
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Introduction to Probability
Approaches to probability • The classical approach • The relative frequency approach • The subjective approach
Mutually exclusive events Two events are mutually exclusive (or disjoint) if the occurrence of one of the events precludes the simultaneous occurrence of the other
The addition rule • If A and B are mutually exclusive events: • p(A or B) = p(A) + p(b) • If A and B are not mutually exclusive: p(A or B) = p(A) + p(b) –p(A and B)
Marginal probabilities p(worker contracts cancer) = 268/1000 = 0.268
Conditional probabilities p(worker contracts cancer | exposed tochemical) = 220/355 = 0.620
Independent events If two events, A and B, are independent: p(A | B) = p(A)
The multiplication rule If A and B are independent events: p(A and B) = p(A) p(B) If A and B are not independent: p(A and B) = p(A) p(B | A)