Correct Answer - Option 4 : 13.5 years
Given:
The average age of a family of 9 members is 20 years.
The age of the youngest son of the family is 8 years.
Calculation:
According to the question,
Sum of present ages of 9 members
⇒ 20 × 9
⇒ 180 years
Total age of a members 8 years ago
⇒ 180 – (9 × 8)
⇒ 108 years
The average age of the members of the family just before the birth
⇒ 108/8
⇒ 13.5 years
∴ The average age of the members of the family just before the birth of the youngest son was 13.5 years.