JEE Main & Advanced Mathematics Probability Question Bank Use of permutations and combinations in probability

  • question_answer
    A bag contains 3 red, 4 white and 5 blue balls. All balls are different. Two balls are drawn at random. The probability that they are of different colour is                                                [EAMCET 1987]

    A)            \[\frac{47}{66}\]                     

    B)            \[\frac{10}{33}\]

    C)            \[\frac{5}{22}\]                       

    D)            None of these

    Correct Answer: A

    Solution :

                       We have  the following three pattern :                    (i) Red, white \[P(A)=\frac{3\times 4}{{}^{12}{{C}_{2}}}\]                    (ii) Red, blue \[P(B)=\frac{3\times 5}{{}^{12}{{C}_{2}}}\]                    (iii) Blue, white \[P(C)=\frac{4\times 5}{{}^{12}{{C}_{2}}}\]                    Since all these cases are exclusive, so the required probability \[=\frac{(12+15+20)}{{}^{12}{{C}_{2}}}=\frac{(47\times 2)}{(12\times 11)}=\frac{47}{66}.\]


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