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 years. Age of the retired teacher is :

55 years

 Age of new teacher = 25 years
Total age decreased = 10 × 3 = 30 years.
∴ Age of the retired teacher = Age of new teacher + Total age decreased
Age of the retired teacher = 25 + 30 = 55 years.