Question

Find the sum of the following APs:
$\left(i\right)$ 2, 7 ,12,....to 10 terms.
$\left(ii\right)$ 0.6, 1.7 ,2.8,....to 100 terms.

Answer 1

$i)$

$2,7,12\dots 10$ terms

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

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

$S_{10}=\frac{10}{2}[4+9(5\left)\right]=245$

$ii)$

$0.6,1.7,2.8\dots$ $100$ terms.

$a=0.6,d=1.1,n=100$

$S_{100}=\frac{100}{2}\left[2\right(0.6)+99(1.1\left)\right]=5505$