JEE Main & Advanced Mathematics Probability Question Bank Definition of probability

  • question_answer
    A bag contains 3 red and 5 black balls and a second bag contains 6 red and 4 black balls. A ball is drawn from each bag. The probability that one is red and other is black, is [AISSE 1986]

    A)                 \[\frac{3}{20}\]    

    B)                 \[\frac{21}{40}\]

    C)                 \[\frac{3}{8}\]       

    D)                 None of these

    Correct Answer: B

    Solution :

               From bag \[A,\,\,P\](red ball)\[={{p}_{1}}=\frac{3}{8}\]            \[P(\]black ball)\[={{p}_{2}}=\frac{5}{8}\]            From bag \[B,\]\[P\](red ball)\[={{p}_{3}}=\frac{6}{10}\]            \[P\](black ball) = \[{{p}_{4}}=\frac{4}{10}\]            Required probability            \[=P\][(red ball from bag \[A\]and black from \[B)\] or (red from bag \[B\] and black from \[A)]\]                                 \[={{p}_{1}}\times {{p}_{4}}+{{p}_{2}}\times {{p}_{3}}=\frac{3}{8}\times \frac{4}{10}+\frac{5}{8}\times \frac{6}{10}=\frac{21}{40}\].


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