KVPY Sample Paper KVPY Stream-SX Model Paper-9

  • question_answer
    A determinant of the second order is made with the elements 0and 1. If \[\frac{m}{n}\]be the probability that the determinant made is non-negative, where m and n are relative primes, then the value of m-n is

    A) 4

    B) 3

    C) 5

    D) 8

    Correct Answer: B

    Solution :

    let \[S\]be the sample space, then \[n\left( S \right)\text{ }=\]total number of determinants that can be made with 0 and 1=\[2\times 2\times 2\times 2=16\]
    \[\because \left| \begin{align}   & a\,\,\,b \\  & c\,\,\,d \\ \end{align} \right|\], each element can be replaced by two types i.e., 0 and 1
    And let E be the event that the determinant made is non-negative.
    Also, E? be the event that the determinant is negative.
    \[\therefore \,E'=\left\{ \left| \begin{align}   & 1\,\,\,1 \\  & 1\,\,\,0 \\ \end{align} \right|,\left| \begin{align}   & 0\,\,\,1 \\  & 1\,\,\,\,1 \\ \end{align} \right|,\left| \begin{align}   & 0\,\,\,\,1 \\  & 1\,\,\,\,\,0 \\ \end{align} \right| \right\}\]
    \[\therefore P\left( E' \right)=3\]
    Then P (E?)\[=\frac{n(E')}{n(S)}=\frac{3}{16}\]
    Hence, the required probability,
    \[P(E)=1-P(E')=1-\frac{3}{16}=\frac{13}{16}=\frac{m}{n}\left[ given \right]\]
    \[\Rightarrow m=13\]and n=16, then n-m=3


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