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NDA 2022
Exam
NDA
Year
2022
Subject
Mathematics
Chapter
Sequences and Series

NDA 2022 · Mathematics · Sequences and Series

The marks obtained by 51 students in a class are in AP with its...

The marks obtained by 51 students in a class are in AP with its first term 4 and common difference 3. What is the mean of the marks?

Options

  1. A67
  2. B71
  3. C75
  4. D79

Correct answer

D. 79

Step-by-step solution

Sn=n2[2a+(n−1)d]=512[8+50×3]=51×1582=51×79\begin{aligned} & S_n=\frac{n}{2}[2 a+(n-1) d] \\ & =\frac{51}{2}[8+50 \times 3]=\frac{51 \times 158}{2}=51 \times 79\end{aligned} Mean ==Snn=51×7951=79==\frac{\mathrm{S}_{\mathrm{n}}}{\mathrm{n}}=\frac{51 \times 79}{51}=79
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