Answer:
[tex]\boxed{\text{6.60 \%}}[/tex]
Explanation:
[tex]\text{Percent error} = \dfrac{\lvert \text{Measured - Actual}\lvert}{ \text{Actual}} \times100 \,\%[/tex]
[tex]\text{\% error} = \dfrac{\lvert 266.5 - 250.0\lvert}{250.0} \times 100 \, \% = \dfrac{\lvert 16.5\lvert}{250.0} \times 100 \, \% = \dfrac{16.5}{250.0} \times 100 \,\%\\\\ = 0.0660 \times 100 \, \% = \textbf{6.60 \%}\\\text{The student's percent error is $\boxed{\textbf{6.60 \%}}$}[/tex]
