Question

Find the sum of all numbers from 1 to 140 which are divisible by 4.

• A. 2530
• B. 2520
• C. 3240
• D. 5410

Answer 1

The correct option is B 2520

Clearly, the numbers from $1$ to $140$ which are divisible by 4 are $4,8,12,...140$.

This is an AP with first term $a=4$, common difference $d=4$ and last term $l=140$.
Let there be $n$ terms in this AP.

Then,
$a_n=140\Rightarrow a+(n-1)d$

$140=4+(n-1)\times 4$

$\therefore n=35$
$\therefore$ required sum $=S_n=\frac{n}{2}[a+l]=\frac{35}{2}[4+140]$

$=2520$