1.  3 yr before, the average age of a family of 5 members was 17 yr. Due to birth of a new child, the average age is same today. The present age of child is :
A. 1 yr
B. 3 yr
C. 2.5 yr
D. 2 yr

Answer: Option D

Explanation:

3 yr before,
Total age of 5 members = 17 x 5 = 85 yr

The present age of all members of family = 85 + 3 x 5 = 100 yr

Let the age of child be x yr.
Present average age of family including the child = (100 + x) / 6

 100 + x = 17
6 1

x = 102 - 100 = 2 yr