Question

the average age of a family of 5 members is 21 years. if the age of the youngest member is 5 years then the average age of the family at the birth of the youngest member was

Answer 1

$\textbf{Given:}$

$\text{Average age the family = 21 years}$

$\text{Sum of the ages of 5 members = }21{\times}5=105$

$\textbf{5 years ago( At the time of youngest member of the family born)}$

$\text{Sum of the ages of the family=Sum of the ages of 4 members}$

$=105-(4{\times}5)-5$

$=105-25=80$

$\text{Average =}\displaystyle\frac{\text{Sum of the ages of 4 members}}{4}$

$\text{Average =}\displaystyle\frac{80}{4}$

$\text{Average =20 years}$

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