Answer:
there are 20 seventh graders in the school band.
Explanation:
If 50% are sixth graders, that means there are 0.5 * 80 = 40 sixth graders.
If 25% are seventh graders, that means there are 0.25 * 80 = 20 seventh graders.
That leaves 80 - 40 - 20 = 20 eighth graders.
Therefore, there are 20 seventh graders in the school band.