Question

The sum up to $23$ terms of the A.P. $5,9,13,17,...$ is

• A. $800$
• B. $912$
• C. $1127$
• D. $1542$

Answer 1

The correct option is C $1127$

Here, $a=5,d=9-5=4,n=23$

Now,
$S_n=\frac{n}{2}[2a+(n-1\left)d\right]\therefore S_{23}=\frac{23}{2}\left[2\right(5)+(23-1\left)4\right]=\frac{23}{2}\times 98=1127$