Out of 10 teachers of a school, one teacher retires and in place of him a new teacher 25 years old joins. As a result of it average age of the teachers reduces by 3 yrs. Age of the retired teacher is:

55 years

Average of 10 teachers decreased by = 3 years and

Total age of 10 teachers decreased by = 10 × 3= 30 years

It means the new teacher's age is 30 years less then the teacher who retired.

Hence, The age of teacher who retired is 25+ 30 = 55 years.

OR

Let initial average be ‘x’

Age of all teachers = 10x

New teacher age = 25

Let retired teacher age = y yrs

New average = x – 3

 \(\frac{10x+25-y}{10}\) = x – 3

10x + 25 – y = 10x – 30

y = 55 yrs.