KVPY Sample Paper KVPY Stream-SX Model Paper-28

  • question_answer
    A is one of the six horses entered for a race and one of the two jockeys B and C ride it. If B rides A, then all the six horses are equally likely to win. If C rides A, then chances of A's win will be trebled. Then, the odds in favour of A's win is

    A) \[2:1\]

    B) \[3:2\]

    C) \[1:2\]

    D) \[2:3\]

    Correct Answer: C

    Solution :

    Let A = Event of A's win
    B = Event of B riding A
    C = Event of C riding A
    Then \[\operatorname{P}\left( \frac{A}{B} \right)=\frac{1}{6}and\,P\left( \frac{A}{C} \right)=3\left( \frac{1}{6} \right)=\frac{1}{2}\]
    Now \[\operatorname{A}=A\cap \left( B\cup C \right)=\left( A\cap B \right)\cup \left( A\cap C \right)\]
    Since B and C are mutually exclusive we have
    \[\operatorname{P}\left( A \right)=P\left( \operatorname{A}\cap \operatorname{B} \right)+\operatorname{P}\left( \operatorname{A}\cap \operatorname{C} \right)\]
    \[=\operatorname{P}\left( B \right)P\left( \frac{A}{B} \right)+\operatorname{P}\left( \operatorname{C} \right)\operatorname{P}\left( A/C \right)\]
    \[\frac{1}{2}\times \frac{1}{6}+\frac{1}{2}\times \frac{1}{2}=\frac{1+3}{12}=\frac{1}{3}\]
    Therefore \[\operatorname{P}\left( \overline{A} \right)=1-\frac{1}{3}=\frac{2}{3}\]
    Hence odds in favour is \[\operatorname{P}\left( E \right):P\left( \overline{\operatorname{E}} \right)=1:2\]


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