###
**(1) + (1 + 1) + (1 + 1 + 1) + ……. + (1 + 1 + 1 + …… n – 1 times) = ……**

A. $\Large\frac{n(n+1)}{2}$
B. $\Large\frac{n(n-1)}{2}$
C. $\boldsymbol{n}^{\mathbf{2}}$
D. n
**Answer: Option B**

## Show Answer

Solution(By Apex Team)

$\begin{aligned}S_{n}=[2 a+(n-1) d] \times \frac{n}{2}\end{aligned}$
$\begin{array}{l}\text{Here,}\\
\text{d}=1\\
\text{a}=1\\
\text{and}\ n-1\ \text{terms}\\
\begin{aligned}
\Rightarrow S_{n-1} &=[2+(n-1-1)] \times \frac{(n-1)}{2} \\
\Rightarrow S_{n-1} &=[2+n-2] \times \frac{(n-1)}{2} \\
&=\frac{n(n-1)}{2}
\end{aligned}\end{array}$

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