The average age of 52 students of a class is 12 years. If the age of the teacher is also included, the average age of the whole group becomes 13 years. The age (in years) of the teacher is:

Correct option is D

Given:
Number of students = 52
Average age of students = 12 years
Average age of the whole group (students + teacher) = 13 years
Formula Used:
Total age = Average age × Number of individuals
Solution:
Total age of 52 students = 12 × 52 = 624
Total number of individuals in the group = 52 + 1 = 53
Total age of the group = 13 × 53 = 689
Age of the teacher = 689 - 624 = 65