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6.3 Conditional Probabilities. Age and Marital Status of women (in thousands). What is the probability of a woman being married? P(married) = 58,929 = .592 99,585. What is the probability of a woman being aged 18 to 24 and married?
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Age and Marital Status of women (in thousands) What is the probability of a woman being married? P(married) = 58,929 = .592 99,585
What is the probability of a woman being aged 18 to 24 and married? P(18 to 24 & married) = 3,046 = .031 99,585
Conditional Probability • Often probabilities will change if we have some other information. • Do you expect the probability of a woman being married given that she is aged 18 to 24 to be the same as the general population? P(married) was .592.
What is the probability of a woman being married given that she is 18 to 24? P(married | 18 to 24) = 3,046/12,614 = .241
P(married) = .592 = P(married | 18 to 24) = .241 = P(married & 18 to 24) = .031 = • The relationship between all three P(married & 18 to 24) = P(married)·P(married|18 to 24) .031 = .592 · .241
General Multiplication Rule • P(A and B) = P(A)·P(B|A) In words this means that for both events to occur, first one one must occur, then, given that the first event has occurred, the second must occur.