There are 120 people in a school canteen. Half of the people in the canteen are in year 11 students.
The number of year 11 students in the canteen is three times the number of year 10 students.
The rest of the people in the canteen are year 9 students.
the number of year 9 students : the number of year 10 students = n : 1
Work out the value of n.
You must show how you get your answer.