Answer
$\displaystyle\sum_{i=1}^{4}\dfrac{1}{4^i}$
Work Step by Step
Using the summation symbol, the expression $
\dfrac{1}{4}+\dfrac{1}{16}+\dfrac{1}{64}+\dfrac{1}{256}
$ can be written as
\begin{array}{l}
\displaystyle\sum_{i=1}^{4}\dfrac{1}{4^i}
\end{array}