Question

The sum of first 20 terms of $AP:8,3,-2,.....$ is:

• A. $-790$
• B. $-970$
• C. $-979$
• D. $-779$

Answer 1

The correct option is A $-790$

$a=8$
$d=3-8=-5$
$S_{20}=\frac{20}{2}[2\times 8+(20-1)\times -5]=10\times -79=-790$