Question

Find the sum of first 10 terms of the arithmetic series if $a_1=2$ and $a_{10}=22$.

• A. $155$
• B. $120$
• C. $165$
• D. $130$

Answer 1

The correct option is B $120$

The sum of $n$ terms of arithmetic sequence can be calculated by the formula

$S_n=\frac{n}{2}(a_1+a_n)$Sn=n2(a1+an)

is the first term and the last term.$n=10$

Given,

First term $a_1=2$

Tenth term $a_{10}=22$

$\Rightarrow S_n=\frac{10}{2}(22+2)$

$\Rightarrow S_n=10\left(12\right)=120$

Hence, option $B$ is correct