Q154 / 270 · NDA 2019 (Phase 2) · Mathematics

If the sum of first $n$ terms of a series is $(n+12)$, then what is its third term?

Correct answer
A
1
B
2
C
3
D
4

Solution

$\begin{array}{ll}\text { } & \text { Given: } S_n=n+12 \\ \because & T_n=S_n-S_{n-1} \\ \therefore & T_3=S_3-S_2 \\ \Rightarrow & T_3=(3+12)-(2+12) \\ \Rightarrow & T_3=1\end{array}$

Hence, the correct answer is option: 'A'.

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