KVPY Sample Paper KVPY Stream-SX Model Paper-10

  • question_answer
    The number of all positive integral roots of the equation, \[px=p+15x,\] \[p\in N\] is:

    A) 3                                 

    B) 4

    C) 5                                 

    D) none of these

    Correct Answer: B

    Solution :

    \[x=\frac{p}{p-15}\]
    \[x=1+\frac{p}{p-15}\]                                        ?(1)
    Roots are positive \[\Rightarrow \] \[\frac{p}{p-15}>0\]
    i.e. \[p\in (-\,\infty ,\,\,0)U(15,\,\,\infty )\] But \[p\in N\] \[\therefore \] \[p\in (15,\,\,\infty )\]
    From (1), For x to be integer \[\frac{15}{p-15}\] should be integer, it is possible
    When \[0<p-15\le 15\] or \[0<p\le 30\] But \[p>15\]
    \[\therefore \]\[p\in (15,\,\,30]\]
    so \[p=16,\] 18, 20, 30
    \[\therefore \]No. of positive integral roots are 4.


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