Given:
The principal approved the event for 200 students.
The number of juniors should be 25% of the number of seniors.
To find:
The number of juniors.
Step-by-step explanation:
Let x be the number of seniors.
According to the problem,

Solve for x we get,

So, the number of seniors is 160.
Therefore, the number of juniors must be,

Final answer:
The number of juniors is 40.