Answer
$∑^{40}_{i=1}i$
Work Step by Step
In summation notation, we are determining the value that is constantly changing, and that will take the place of the $i$ term. In addition, we look at the summation to see how many sums we will need to take, and that will be our upper bound of summation. The other constant terms will stay constant in this notation.
$1+2+3+...+40$
$∑^{40}_{i=1}i$