10th Class Mathematics Probability Question Bank Probability

  • question_answer
    If one number is selected from the first 70 natural numbers, the probability that the number is a solution of \[{{x}^{2}}+2x>4\] is

    A)  \[\frac{69}{70}\]          

    B)  \[\frac{1}{70}\]

    C)  \[1\]                            

    D)  \[0\]

    Correct Answer: A

    Solution :

    (a): \[{{x}^{2}}+2x-4>0\] root \[\alpha ,\beta =\frac{-2\pm \sqrt{4+16}}{2}=\frac{-2\pm 2\sqrt{5}}{2}=-1\pm \sqrt{5}\] or,        \[\left\{ x-\left( -1+\sqrt{5} \right) \right\}\left\{ x-\left( 1-\sqrt{5} \right) \right\}>0\]  \[\therefore \]      \[x\in \left( -\infty ,-1-\sqrt{5} \right)\cup \left( -1+\sqrt{5},\infty  \right)\] \[\therefore \] Within natural numbers, only 1 is not the solution \[\therefore \]      \[P=\frac{69}{70}\]                  


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