The average age of 57 students of a class is 13 years. If the age of the teacher is also included, the average age of the whole group becomes 14 years. The age (in years) of the teacher is:

Correct option is D

Given:

The average age of 57 students is 13 years.

Average age of 57 students and 1 teacher = 14 years. 

Formula Used: ​

Total sum = Average $$\times$$ Number of terms

Solution: ​

Total age of 57 students = 57 $$\times$$ 13 = 741 years

Total age of  58 students and 1 teacher = 58 $$\times$$ 14 =  812 years

Then,

Teacher's age = 812 - 741 = 71 years