Since there are 4 sick students with flu for each sick student with other illness, then, there are 4 students with flu for each 5 sick students.
Multiply the ratio 4:5, which is the proportion of students with flu to sick students, by the total amount of sick students, to find how many students had the flu:
![(4)/(5)*60=48](https://img.qammunity.org/2023/formulas/mathematics/college/q07uyysrqntc66u7rffstc33h0vbcf8w7n.png)
Therefore, 48 students had the flu.