The average age of a husband and wife, who were married 3 years ago, was 35 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 30 years today. The age of the child is:

14 years

Average age of a husband and wife, who were married 3 years ago = 35 years

Sum of the present age of husband and wife
= 2 × 35 + 2 × 3 = 76 years

The average present age of husband, wife and a child = 30 years

Sum of the present age of husband, wife and child = 3 × 30 = 90 years

∴ Child’s present age = 90 – 76 = 14 years