Answer
$\sum_{i=1}^{n} \dfrac{i}{9^i}$
Work Step by Step
In order to set up the summation notation, we must calculate that value which keeps constantly changing. That value will be designated as the $i$ term. The remaining terms would remain constant in the summation notation.
Thus, we get the summation notation:
$\sum_{i=1}^{n} \dfrac{i}{9^i}$
