Answer
$\dfrac{33}{2}$
Work Step by Step
The expression $
\displaystyle\sum_{i=3}^7 2^{i-4}
$ evaluates to
\begin{array}{l}
2^{3-4}+2^{4-4}+2^{5-4}+2^{6-4}+2^{7-4}
\\\\=
2^{-1}+2^{0}+2^{1}+2^{2}+2^{3}
\\\\=
\dfrac{1}{2}+1+2+4+8
\\\\=
\dfrac{33}{2}
.\end{array}
