The average age of 39 students of a class is 39 years. If the age of the teacher is also included, the average age of the whole group becomes 40 years. The age (in years) of the teacher is:
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. 79.
Average age of 39 students = 39 years
Total age of 39 students = 39 × 39 = 1521
New average with teacher = 40 years
Total people = 39 + 1 = 40
Total age of group = 40 × 40 = 1600
Teacher's age = 1600 − 1521 = 79