Question

The average age of a family of 9 members is 22 years. Surya is the youngest and his age is 6 years, then what was the average age of the family just before Surya was born?

Answer 1

Total number of members in the family = 9

$\boxed{ \mathsf{Average = \dfrac{sum\:of\:quantity}{Number\:of \:quantit}}}$

Therefore,

= > 22 years = ( sum of ages of 9 members ) / ( 9 )

= > 22 years x 9 = sum of ages of 9 members

= > 198 years = sum of ages of 9 member

In question we have to find the average age of the family before surya was born. In simple words, we have to find the average age of the family before 6 years( as surya is 6 years old ).

As surya was not born 6 years before, he wouldn't be counted in the members of the family.

Therefore total number of members in the family before 6 years is 9 - 1 = 8

Therefore,

= > Average age of family at  that time = ( sum of 9 members - age of surya - ( 6 x 8 ) ) / 8

= > Average age of family at that time = ( 198 - 6 - 42 ) / 8

= > Average age of famliy at that time = ( 144 ) / 8

= > Average age of family at that time = 18

Therefore, average age of family was 18 years.