SSC Sample Paper Mock Test-9 SSC CGL Tear-II Paper-1

  • question_answer
    \[\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{n\,\,(n+1)}=?\]

    A)  \[\frac{1}{n}\]

    B)  \[\frac{1}{n+1}\]

    C)  \[\frac{2\,\,(n-1)}{n}\]

    D)  \[\frac{n}{n+1}\]

    Correct Answer: D

    Solution :

    \[{{T}_{n}}=\frac{1}{n\,\,(n+1)}=\left( \frac{1}{n}-\frac{1}{n+1} \right)\] \[\therefore \] Given sum\[=\left( 1-\frac{1}{2} \right)+\left( \frac{1}{2}-\frac{1}{3} \right)+\left( \frac{1}{3}-\frac{1}{4} \right)+\] \[\left( \frac{1}{4}-\frac{1}{5} \right)+...+\left\{ \frac{1}{n}-\frac{1}{(n+1)} \right\}=\left\{ 1-\frac{1}{n+1} \right\}=\frac{n}{(n+1)}\]


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