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

  • question_answer
    Two persons each make a single throw with a die. The probability they get equal value is\[{{p}_{1}}\]. Four persons each make a single throw and probability of three being equal is\[{{p}_{2}}\], then

    A)            \[{{p}_{1}}={{p}_{2}}\]     

    B)            \[{{p}_{1}}<{{p}_{2}}\]

    C)            \[{{p}_{1}}>{{p}_{2}}\]     

    D)            None of these

    Correct Answer: C

    Solution :

                       \[{{p}_{1}}=\frac{6}{36}=\frac{1}{6}\]            To find \[{{p}_{2}},\] the total number of ways \[={{6}^{4}}\]and since two numbers out of 6 can be selected in \[{}^{6}{{C}_{2}}\] ways i.e. 15 ways and corresponding to each of these ways, there are 8 ways e.g., \[(1,\,\,1,\,\,1,\,\,2)\,\,(1,\,\,1,\,\,2,\,\,1)\,.....\]                    Thus favourable ways \[=15\times 8=120\]                    Hence \[{{p}_{2}}=\frac{120}{{{6}^{4}}}=\frac{5}{54}\]. Hence \[{{p}_{1}}>{{p}_{2}}.\]


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