To find the average age 4 years ago:
Step 1: Calculate the current average age
Sum of ages = 150
Number of students = 10
Current average age = Sum of ages / Number of students
= 150 / 10
= 15
Step 2: Calculate the average age 4 years ago
Average age 4 years ago = Current average age - 4
= 15 - 4
= 11
So, the average age of the students 4 years ago was:
11