probability (P) - numerical value sample space (S) - well defined SET of possible outcomes (of an experiment) event (A,B, etc) - well defined SET of outcomes (of an experiment) with a probability is subset of sample space (S) experiment - any procedure that can be infinitely repeated, has a sample space #1 probability of sample space (S) = P(S) = 1 #2 probability of occurence of event (A) = P(A) is beteen 0 and 1, both inclusive, 0<=P(A)<=1 probability of non-occurence of event (A) = P(A') is beteen 0 and 1, both inclusive, 0<=P(A)<=1 P(A) = number of favourable outcomes / total number of outcomes P(A) = |A| / |S| if A and A' is S then P(A) + P(A') = P(S) => P(A) + P(A') = 1 => P(A') = 1 - P(A) Simple event Compound event = combination of simple events A U B = occurence of A or B A n B = occurence of A and B P(A U B) = P(A) + P(B) - P(A n B) Mutually exclusive (disjoint) events = No common outcomes of between A and B A n B = Pi (empty set) P(A n B) = 0 P(A U B) = P(A) + P(B) - P(A n B) => P(A U B) = P(A) + P(B) - 0 => P(A U B) = P(A) + P(B)