Teacher:The task is to generate the correct answer for a given math problem.
Teacher: Now, understand the problem? Solve this instance: Problem: exactly 3 / 7 of the people in the room are under the age of 21 , and exactly 5 / 10 of the people in the room are over the age of 65 . if the total number of the people in the room is greater than 50 and less than 100 , how many people in the room are under the age of 21 ?
Student:
30