From the given question:
The percentage of students who chose to study Spanish their senior year is 48%.
Now,
Let the total number of students is x
Since there were 204 such students that chose to study Spanish their senior year
According to the question,
[tex]\begin{gathered} 48\%\text{ of x=204} \\ 0.48x=204 \\ x=\frac{204}{0.48} \\ x=425 \end{gathered}[/tex]Then,
The number of students who chose not to take Spanish :
[tex]425-204=221[/tex]Hence, 221 students who do not choose to take Spanish.