JEE Main & Advanced Mathematics Probability Question Bank Binomial distribution

  • question_answer
    A bag contains 2 white and 4 black balls. A ball is drawn 5 times with replacement. The probability that at least 4 of the balls drawn are white is                                   [AMU 2001]

    A)                 \[\frac{8}{141}\]  

    B)                 \[\frac{10}{243}\]

    C)                 \[\frac{11}{243}\]

    D)                 \[\frac{8}{41}\]

    Correct Answer: C

    Solution :

               Probability for  white ball \[=\frac{2}{6}=\frac{1}{3}\]            Probability for black ball \[=\frac{4}{6}=\frac{2}{3}\] \[\therefore \]Required probability                   \[={{\,}^{5}}{{C}_{5}}{{\left( \frac{1}{3} \right)}^{5}}\,{{\left( \frac{2}{3} \right)}^{0}}\,+{{\,}^{5}}{{C}_{4}}{{\left( \frac{1}{3} \right)}^{4}}\left( \frac{2}{3} \right)\]                                                 \[={{\left( \frac{1}{3} \right)}^{4}}\,\left[ \frac{1}{3}+5.\,\frac{2}{3} \right]\]\[=\frac{11}{{{3}^{5}}}=\frac{11}{243}\].


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