Question

Find the sum of first $10$ terms of AP $3,7,11,...$.

Answer 1

The given series is $3,7,11,....$

Here $a=3,d=7-3=4$

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

$S_{10}=\frac{10}{2}\left(2\right(3)+9(4\left)\right)$ ............ sum of first $10$ terms

$S_{10}=5(6+36)=210$