Question

Sum of all the integers between $100$ and $1000$ which are divisible by $7$ is:

• A. $70336$
• B. $70400$
• C. $78029$
• D. none of the above

Answer 1

The correct option is A $70336$

$S=105+112+.....994$ and $105+(n-1)7=994\Rightarrow 105+7n-7=994\Rightarrow n=128$
$s=\frac{n}{2}(a+l)=\frac{128}{2}(105+994)=70336$