3 yr ago, the average age of a family of 5 members was 17 yr. Even after the birth of a child, the aveage is same today. Find out the age of child.

3 yr ago, total age of 5 members of the family = 17 x 5 = 85 yr
Present age of all the members of the family = 85 + 3 x 5 = 100 yr
Let the age of the child = N yr
Present avrage age of family = (100 + N) / 6
[At present total number of members = 5 + 1 = 6]
17 = 100N / 6
⇒ 102 = 100 + N
∴ N = 2 yr