11th Class Mental Ability Probability Question Bank Question - Probability

  • question_answer
    A bag contains 4 white, 5 red and 6 blue balls. Three balls are drawn at random from the bag. The probability that all of them are red, is:

    A) \[\frac{1}{22}\]

    B) \[\frac{3}{22}\]

    C) \[\frac{2}{91}\]

    D) \[\frac{2}{77}\]

    E) None of these

    Correct Answer: C

    Solution :

    Explanation Option (c) is correct. Let S be the sample space. Then, n (S) = number of ways of drawing 3 balls out of 15 \[{{=}^{15}}{{C}_{3}}=\frac{(15\times 14\times 13)}{(3\times 2\times 1)}=455\] Let E = event of getting all the 3 red balls. \[\therefore \,\,\,\,\,\,\,\,\,\,\,\,n\,(E){{=}^{5}}{{C}_{3}}{{=}^{5}}{{C}_{2}}=\frac{(5\times 4)}{2\times 1}=10\] \[\therefore \,\,\,\,\,\,\,\,\,\,\,\,P\,(E)=\frac{n(E)}{n(S)}=\frac{10}{455}=\frac{2}{91}\,\,\,.\]


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