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SSC Sample Paper Mock Test-18 SSC CGL Tear-II Paper-1

  • question_answer
    \[(45+46+47+...+113+114+115)=?\]

    A) 5600

    B)  5656   

    C)  5680   

    D)  4000

    Correct Answer: C

    Solution :

    Sum of first n natural numbers \[=(1+2+3+...+n)\] \[=\frac{1}{2}n\,\,(n+1)\]             \[(45+46+47+...+114+115)\]    \[=(1+2+3+...+44+45+46+...+114+115)\]\[-(1+2+3...+44)\]             \[=\left( \frac{1}{2}\times 115\times 116 \right)-\left( \frac{1}{2}\times 44\times 45 \right)\]             \[=(115\times 58)-(22\times 45)=(6670-990)=5680\]


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