Question

The sum of the arithmetic series :
$5+11+17+......+95$ is

• A. $600$
• B. $700$
• C. $800$
• D. $500$

Answer 1

Answer: (C)

$800$

Given, $5+11+17+......+95$

$\therefore a=5,d=6,l=95$

By using $a_n=a+(n-1)d$

$95=5+(n-1)6$

$\Rightarrow 90=6(n-1)$
$\Rightarrow n-1=15$

$\Rightarrow n=16$
$S_{16}=\frac{n}{2}\{a+1\}$

$=\frac{16}{2}\{5+95\}$

$=800$