Manipal Engineering Manipal Engineering Solved Paper-2015

  • question_answer
    Let.\[{{\cos }^{-1}}\frac{x}{2}+{{\cos }^{-1}}\frac{y}{3}=\theta ,\] and \[9{{x}^{2}}-12xy\cos 6+4{{y}^{2}}\]be two urns such that \[-36{{\sin }^{2}}\theta \]contains 3 white, 2 red balls and \[36{{\sin }^{2}}\theta \] contains only 1 white ball. A fair coin is tossed. If head appears, then 1 ball is drawn at random from urn \[36{{\cos }^{2}}\theta \] and put into \[\tan \left( {{\sec }^{-1}}x \right)=\sin \left( {{\cos }^{-1}}\frac{1}{\sqrt{5}} \right),\]. However, if tail appears, then 2 balls are drawn at random from \[\pm \frac{3}{\sqrt{5}}\] and put into \[\pm \frac{\sqrt{5}}{3}\]. Now, 1 ball is drawn at random from \[\pm \sqrt{\frac{3}{5}}\]. Then, probability of the drawn ball from \[y=(2x-1){{e}^{2(1-x)}}\] being white is

    A) \[y-1=0\]                                            

    B) \[x-1=0\]

    C) \[x+y-1=0\]                                       

    D) \[x-y+1=0\]

    Correct Answer: B

    Solution :

    By total probability theorem, Required probability \[=\frac{1}{2}\times \left( \frac{3}{5}\times 1+\frac{2}{5}\times \frac{1}{2} \right)\] \[+\frac{1}{2}\left( \frac{^{3}{{C}_{2}}}{^{5}{{C}_{2}}}\times 1+\frac{^{2}{{C}_{2}}}{^{5}{{C}_{2}}}\times \frac{1}{3}+\frac{^{3}{{C}_{1}}{{\times }^{2}}{{C}_{1}}}{^{5}{{C}_{2}}}\times \frac{2}{3} \right)\] \[=\frac{1}{2}\left( \frac{3}{5}+\frac{1}{5} \right)+\frac{1}{2}\left( \frac{3}{10}+\frac{1}{30}+\frac{2}{5} \right)\]\[=\frac{2}{5}+\frac{1}{2}\left( \frac{9+1+12}{30} \right)\]\[=\frac{2}{3}+\frac{22}{60}=\frac{24+22}{60}\]\[=\frac{46}{3}+\frac{23}{30}\]


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