Question

The average age of 40 students in a class is 15 years. if the age of teacher is also excluded, the average becomes 10 years, find the age of the teacher.

Answer 1

 teacher's age is 15 years, there is no change in the average.  
Age of teacher = Average age of all + Total increase in age
= 10+ (1 x 40 ) = 50 years

Answer 2

Concept:

Here we will apply the concept of multiplication and addition.

Given:

The average age of 40 students in a class is 15 years.

To find:

The age of the teacher.

Solution:

The average age of 40 students in a class is 15 years. We have to find the age of the teacher.

So, let's assume the teacher's age is x years

Sum of the age of 40 students = $40*15=600$

If the teacher is included in the sum of ages of the 40 students, then the total number becomes 41, and the average age of 41 students becomes 16.

So, the age of the teacher =

actual age of 41 persons = 41*16

$x+600=41*16\\x+600=656\\x=656-600\\x=56$

∴The age of the teacher is 56 years.

#SPJ2