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Unformatted text preview: If X and Y are independent random variables then Z=X+Y with the means adding up. Formula for poisson dist-(1) P(X=k)= e^-u (u^k)/k ! [where e= 2.71828] (2) Excel- poissondist (k,u,0) for P(X=k) and poissondist(k,u,1) for P(X</k) Note if we need to get P(75 </ X </ 90) we do poissondist(90,84,1) poissondist(74,84,1) and not 75. Conditional probability of B |A is the probability of an event B occurring given that A has definitely occurred. The general multiplication rule for this is P(A) X P(B |A). This is like multiplying across tree diagrams. (Extended version of this would be P(A and B and C)= P(A) X P(B |A) X P(C |A and B ). If A and B are independent then P(A |B)= P(A) since knowing B tells us nothing about the probability of A. Bayes rule- P(A |B)= P(A and B)/P(B). In other words, P(A |B)= P(A) x P(B |A)/P(A)xP(B |A) + P(Ac)xP(B |Ac)...
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