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
Average age of the family = 33
Total age of the 5 members = 5*33 = 165 years
Sum of ages of the 5 members 9 years ago = 165 - 9*5 = 120
Number of members in the family 9 years ago = 4
Average age 9 years ago = $$\frac{120}{4}$$ = 30
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