In a family of 5 members, the average age at present is 33 years. The youngest member is 9 years old. The average age of the family just before the birth of the youngest members was :

According to the question,
Average age of 5 members today = 33 years
Sum of ages of 5 members today = 33 × 5 = 165 years
If the youngest member is 9 year old
∴ Sum of the age of 4 members before the birth of youngest child
= 165 - 9 - 4 × 9
= 120 years
∴ Average = $$\frac{120}{4}$$ = 30 years