Let x represent the total number of stdents that has all grades in the school.
There are three grades in the school. One grade has 1/3 of the students, this means that number of students that belongs tho this grade is 1/3 × x = x/3
One grade has 1/4 of the students, this means that number of students that belongs to this grade is 1/4 × x = x/4
Total number of students in both grades would be x/3 +/x/4 = 7x/12
The number of students in the remaining grade would be
x - 7x/12 = 5x/12
fraction of students in the remaining grade would be
