Question

3 years back the average age of a family with 5 members was 17 years. After 5 years average age of the family remains the same even after the birth of child. What is the age of the child now?

Answer 1

3 years ago, the average age of a family of 5 members was 17 years.
This means that the sum of their ages was (5)(17) = 85 years.
A baby was born (meaning that there are now 6 family members). We're told that the present average age of the family members is the same.
This means that the sum of the ages is (6)(17) = 102 years.
Since each of the original 5 family members has aged 3 years since the initial average was calculated, the sum of their present ages is
85 + (5)(3) = 100.
Since the current sum of the 6 family members is 102, the baby is 102-100 = 2 years old.