The average age of 5 members of a family is 24 years. If the youngest member is 8 years old, then what was the average age (in years) of the family at the time of the birth of the youngest member?
The average age of 5 members of a family is 24 years
$$\Rightarrow$$ total age of 5 members = $$5\times 24=120$$
age of youngest one = 8 years
before the birth of youngest one means before 8 years,
their total age = $$120 - 5\times 8=120-40=80$$
at that time, there would be 4 persons only.
hence, average = $$\frac{80}{4}=20.$$
so the answer is option B.
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