The average age of boys in a school of 750 boys is 15.4 years. After 50 boys left the school, the average age is reduced to 15.3 years. Find the value of average age of those 50 boys.

The average age of 30 boys in a class is 15 years. If we include the age of two teachers the average age increases by 1. Find the sum of ages of the two teachers.

The average age of 30 boys in a class is 15 years. One boy aged 20 years, left the class, but two new boys came in his place whose ages differ by 5 years. If the average age of all the boys now in the class still remains 15 years, the age of the younger newcomer is:

The average age of 30 boys in a class is 15 years. One boy, aged 20 years, left the class, but two new boys came in this place whose age differ by 5 years. If the average age of all boys now in the class becomes 15 years, the age of the younger newcomer is :