Answer
$\sum_{i=3}^{7}\sqrt{i}$
Work Step by Step
We contract the sum into sigma notation by noting that it follows the pattern of a sum of square roots (e.g. $\sqrt{i}$) from 3 to 7:
$\displaystyle \sqrt{3}+\sqrt{4}+\sqrt{5}+\sqrt{6}+\sqrt{7}=\sum_{i=3}^{7}\sqrt{i}$