Question

What is sum of $30$ terms of the given arithmetic series: $12+24+36+...?$

• A. $2580$
• B. $3580$
• C. $4580$
• D. $5580$

Answer 1

Answer: (D)

$5580$

$S_n=\frac{n}{2}[2a+(n-1\left)d\right]$
$\Rightarrow S_{30}=\frac{30}{2}[2\times 12+(30-1\left)12\right]$
$\Rightarrow S_{30}=15[24+348]$
$\Rightarrow S_{30}=15\left[372\right]$
$\Rightarrow S_{30}=5580$