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 member was

Sum of the present ages of family members

= 33 × 5 = 165 years

9 years ago,

Sum of their ages = 165 – 9 × 5 = 120 years

$herefore$ Required average age $=frac{120}{4}=30$ years