The average age of a group is increased by 6 years when a person whose age is 24 years was replaced by a person whose age is 66. Find the number of persons in the group.

8 9 6 7

7

Lets assume average age of group = x Number of people in group = n ⇒ \(\frac{ (nx - 24 + 66)}{n}\) = x + 6 ⇒ nx + 42 = nx + 6n ⇒ n= 7 ∴ Number of people in group are 7.