JEE Main & Advanced Mathematics Sequence & Series Question Bank Harmonic Progression

  • question_answer
    The fifth term of the H.P., \[2,\ 2\frac{1}{2},\ 3\frac{1}{3},.............\] will be  [MP PET 1984]

    A) \[5\frac{1}{5}\]

    B) \[3\frac{1}{5}\]

    C) 1/10

    D) 10

    Correct Answer: D

    Solution :

    Series, \[2,\ 2\frac{1}{2},\ 3\frac{1}{3},.......\]are in H.P. \[\Rightarrow \]\[\frac{1}{2},\ \frac{2}{5},\ \frac{3}{10},.......\] will be in A.P. Now first term \[a=\frac{1}{2}\] and common difference \[d=-\frac{1}{10}\] So, \[=\frac{2}{3}(10+{{10}^{2}}+{{10}^{3}}+..........+\] term of the A.P.  \[=\frac{1}{2}+(5-1)\left( -\frac{1}{10} \right)=\frac{1}{10}\] Hence \[{{5}^{th}}\] term in H.P. is 10.


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