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NDA 2019
Exam
NDA
Year
2019
Subject
Mathematics
Chapter
Sequences and Series

NDA 2019 · Mathematics · Sequences and Series

What is the value of 1-2+3-4+5- +101 ?

What is the value of 1−2+3−4+5−…+101?1-2+3-4+5-\ldots+101 ?

Options

  1. A51
  2. B55
  3. C110
  4. D111

Correct answer

A. 51

Step-by-step solution

S=(1−2)+(3−4)+…+101⇒−1−1−1…+101⇒−50+101⇒S=51\begin{aligned} & S=(1-2)+(3-4)+\ldots+101 \\ & \Rightarrow-1-1-1 \ldots+101 \\ & \Rightarrow-50+101 \\ & \Rightarrow S=51\end{aligned}
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