Question

Find the sum of the following A.P
$2,7,12,.....$ to $10$ terms

Answer 1

$2,7,12,--------10,$ terms

$\therefore a=2,d=5,n=10$

$S_n=\frac{n}{2}[2a+(n-1\left)d\right]$

$S_{10}=\frac{10}{2}\left(2\right(2)+(10-1\left)5\right)$

$=5(4+9\times 5)$

$=5(4+45)$

$=5\times 49$

$=245$