Question

If $n$th term of an A.P is $a_n=2-3n$, then sum of first $25$ terms is :

• A. $-911$
• B. $-882$
• C. $-925$
• D. None of the above

Answer 1

Answer: (C)

$-925$

Given:

$a_n=2-3n$

$\therefore S_n=\sum a_n=\sum (2-3n)$

$\therefore S_n=2n-3\frac{n(n+1)}{2}$

$\therefore S_{25}=2\times 25-3.\frac{25\times 26}{2}=-925$

Hence, the answer is $-925$.