JEE Main & Advanced Mathematics Binomial Theorem and Mathematical Induction Question Bank Mathematical induction and Divisibility problems

  • question_answer
    For a positive integer n, Let\[a\,(n)=1+\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+....+\frac{1}{({{2}^{n}})-1}\]. Then [IIT 1999]

    A) \[a\,(100)\le 100\]

    B) \[a\,(100)>100\]

    C) \[a\,(200)\le 100\]

    D) \[a\,(200)>100\]

    Correct Answer: A

    Solution :

     It can be proved with the help of mathematical induction that \[\frac{n}{2}>a(n)\le n\]. \[\therefore \]\[\frac{200}{2}\]< \[a(200)\] \[\Rightarrow \] \[a(200)\]>100 and \[a(100)\le 100\].


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