The average age of 22 students of a class is 47 years. If the age of the teacher is also included, the average age of the whole group becomes 48 years. The age (in years) of the teacher is:

Correct option is C

Given:
The average age of 22 students = 47 years
The average age of the whole group (22 students + teacher) = 48 years
Formula Used:
​$$\text{Average} = \frac{\text{Sum of ages}}{\text{Number of individuals}}$$​​
Solution:
​Let the age of the teacher be T.
Sum of ages of 22 students = 22 × 47 = 1034 years
Sum of the ages of the 23 individuals (22 students + teacher) = 23 × 48 = 1104 years
Age of the teacher, T = 1104 - 1034 = 70 years
Thus, the age of the teacher is 70 years.