Average age of a group of 15 boys is 24 years. A boy having age 13 years leaves the group. A new boy joins the group and the average increases by 1 year. What is the age of the new boy?

Correct option is A

Given:
Number of boys in the group = 15
Average age of the group = 24 years
Age of the boy who left = 13 years
New average = 24 + 1 = 25 years
Formula Used:
Total age = Average * Number of boys
Age of the new boy = (New total age) - (Old total age) + (Age of boy who left)
Solution:
Old Total Age = Average $$\times$$​ Number of Boys 
Old Total Age = 24 $$\times$$ 15 ​ = 360
New Total Age = New Average $$\times$$ Number of Boys ​
New Total Age = 25$$\times$$ 15 = 375
Age of New Boy = New Total Age - Old Total Age + Age of Boy Who Left 
Age of New Boy = 375 - 360 + 13 = 28
Thus, the age of the new boy is 28 years.