J & K CET Engineering J and K - CET Engineering Solved Paper-2005

  • question_answer
    Two cards are drawn successfully with replacement from a well shuffled deck of 52 cards, then the mean of the number of aces is

    A)  \[1/13\]

    B)  \[3/13\]

    C)  \[2/13\]

    D)  None of the above

    Correct Answer: C

    Solution :

    Case  I. When zero ace \[{{P}_{1}}({{x}_{1}}=0)=\frac{48}{52}\times \frac{48}{52}={{\left( \frac{12}{13} \right)}^{2}}\] Case II.  When one ace \[{{P}_{2}}({{x}_{2}}=1)=\frac{4}{52}\times \frac{48}{52}+\frac{48}{52}\times \frac{4}{52}\] \[=\frac{12}{{{(13)}^{2}}}+\frac{12}{{{(13)}^{2}}}=\frac{24}{{{(13)}^{2}}}\] Case III.  When two aces \[{{P}_{3}}({{x}_{3}}=2)=\frac{4}{52}\times \frac{4}{52}={{\left( \frac{1}{13} \right)}^{2}}\] Now,  mean \[={{P}_{1}}{{x}_{1}}+{{P}_{2}}{{x}_{2}}+{{P}_{3}}{{x}_{3}}\] \[={{\left( \frac{12}{13} \right)}^{2}}\times 0+\frac{24}{{{(13)}^{2}}}\times 1+{{\left( \frac{1}{13} \right)}^{2}}\times 2\] \[=\frac{24+2}{169}=\frac{26}{169}=\frac{2}{13}\]


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