Final answer:
The 6th graders filled 38% of the seats in the theater.
Step-by-step explanation:
To find the percentage of seats in the theater that were filled by the 6th graders, we need to divide the number of seats filled by the 6th graders (1178) by the total number of seats in the theater (3100) and then multiply by 100.
So the calculation would be: (1178 / 3100) * 100 = 38%.
Therefore, 38% of the seats in the theater were filled by the 6th graders on the trip.