There are 200 students in 6th period lunch.
The ratio of 7th graders to 8th graders is 4 to 5.
Let's find the percentage of the students are 7th graders:
=> 200 / 9 = 22.22
=> 22.22 * 5 = 111.11 or 111
=> 22 * 4 = 88.88 or 89
=> 4 : 5 or 89 : 111
7th grader = 55%