The average age of a husband and wife, who were married 4 years ago, was 25 years at the time of their marriage. The average age of the family consisting of husband, wife and a child, born during the interval is 20 years today. The age of the child is:

2 years

Average age of a husband and wife, who were married 4 years ago = 25 years

Sum of the present age of husband and wife
= 2 × 25 + 2 × 4 = 58 years

The average present age of husband, wife and a child = 20 years

Sum of the present age of husband, wife and child = 3 × 20 = 60 years

∴ Child’s present age = 60 – 58 = 2 years