The average age of 40 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 C

Given:

The average age of 40 students is 12 years.

Average age of 40 students and 1 teacher = 13 years. 

Formula Used: ​

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

Solution: ​

Total age of 40 students = 12 $$\times$$ 40 = 480 years

Total age of 40 students and 1 teacher = 41 $$\times$$ 13 =  533 years

Then,

Teacher's age = 533 - 480 =53 years