Find the number of students above twelve years of age in your class. Then, find the ratio of the number of students with age above twelve years and the remaining students.
suppose there are 40 students in the class and 5 students are above 12 years, then there are 40-5=35 students below or equal to 12 years.
Then he ratio of the number of students with age above twelve years and the remaining students = 5:35=1:7