{"id":3910,"date":"2021-08-10T02:29:49","date_gmt":"2021-08-10T02:29:49","guid":{"rendered":"https:\/\/mathemerize.com\/?p=3910"},"modified":"2021-11-27T23:18:06","modified_gmt":"2021-11-27T17:48:06","slug":"conditional-probability","status":"publish","type":"post","link":"https:\/\/mathemerize.com\/conditional-probability\/","title":{"rendered":"Formula for Conditional Probability"},"content":{"rendered":"
Here, you will learn formula for conditional probability and properties of conditional probability with examples.<\/p>\n
Let’s begin –<\/p>\n
Let A and B be two events associated with a random experiment. Then, the probability of occurrence of event A under the condition that B has already occured and P(B) \\(\\ne\\) 0, is called the conditional probability and it is denoted by P(A\/B). Thus, we have<\/p>\n
\nP(A\/B) = Probability of occurrence of A given that B has already occurred<\/p>\n
P(A\/B) = \\({P(A\\cap B)}\\over P(B)\\) = which is called Conditional Probability of A given B.<\/p>\n<\/blockquote>\n
Similarly, P(B\/A) when P(A) \\(\\ne\\) 0 is defined as the probability of occurrence of event B when A has already occurred.<\/p>\n
\nP(B\/A) = \\({P(A\\cap B)}\\over P(A)\\) = which is called Conditional Probability of B given A.<\/p>\n<\/blockquote>\n
Example<\/strong><\/span> : Let there be a bag containing 5 white and 4 red balls. Two balls are drawn from the bag one after the other without replacement.<\/p>\n
Solution<\/span><\/strong> : Consider the following events :<\/p>\n
A = Drawing a white ball in the first draw,<\/p>\n
B = Drawing a red ball in the second draw<\/p>\n
Now,<\/p>\n
P(B\/A) = Probability of drawing a red ball in second draw given that a white ball has already been drawn in the first draw<\/p>\n
\\(\\implies\\) P(B\/A) = Probability of drawing a red ball from a bag containing 4 white and red balls<\/p>\n
\\(\\implies\\) P(B\/A) = \\(4\\over 8\\) = \\(1\\over 2\\)<\/p>\n
For this random experiment P(A\/B) is not meaningful because A cannot occur after the occurence of event B.<\/p>\n
Properties of Conditional Probability<\/strong><\/h4>\n
(i)<\/strong>\u00a0 Let A and B be two events associated with sample space S, then 0 \\(\\le\\) P(A\/B) \\(\\le\\) 1.<\/p>\n
(ii)<\/strong> If A is an event associated with the sample space S of a random experiment, then P(S\/A) = P(A\/A) = 1<\/p>\n
(iii)<\/strong> Let A and B be two events associated with a random experiment and S be the sample space, if C is an evnt such that P(C) \\(\\ne\\) 0, then<\/p>\n
P(\\((A\\cup B)\/C\\)) = P(A\/C) + P(B\/C) – P(\\((A\\cap B)\/C\\))<\/p>\n
In Particular, if A and B are mutually exclusive events, then<\/p>\n
P(\\((A\\cup B)\/C\\)) = P(A\/C) + P(B\/C)<\/p>\n
(iv)\u00a0<\/strong> If A and B are two events associated with a random experiment, the P(A’\/B) = 1 – P(A\/B)<\/p>\n\n\n