3 out of 4 students mean
3/4th students were wearing shirts.
Total students = 600
So,
3/4th of 600 students were wearing shirt.
Let us calcualte (3/4)th of 600:
[tex]\begin{gathered} \frac{3}{4}\times600 \\ =\frac{3\times600}{4} \\ =\frac{1800}{4} \\ =450 \end{gathered}[/tex]Answer450 students