PROBLEM SOLVING IN MATHEMATICS
posted by alya .
the average age of a group of teachers and student is 20. the average age of the teachers is 35. the average age of the students is 15. what is the ratio number of teacher to number of students ?

Let x be the number of students and y be the number of teachers. You want to know y/x.
The sum of the products of people and there ages can be written as
(x + y)*20 or 15 x + 35 y.
Therefore
(x + y)*20 = 15 x + 35 y
5x = 15 y.
y/x = 1/3 is the teacher/student ratio.