Question

five years ago mean age of a family was 25 years what is the present mean age of the family

Answer 1

Let there be n number of members in your family.
Therefore the sum of ages of all the members 5 years ago = Mean×Number
=25n
At present, the ages of all the members have increased by 5 years, therefore present sum of ages = 25n + 5n [5 year for each member]
= 30n
New (present) average=30n/n
= 30 years [Answer]
Note: If average of n numbers is av, then new average (1) when every number is increased by k is (av+k).
(2) When every number is multiplied by k is (av×k).

Hope this helps. Thanks!

Answer 2

Answer:

No. of members in a family=x

Mean age of the family=25 years

Mean = sum of observations / number of observations

25= sum of observations/x

sum of observations =25 x

After 5 years the sum of observations will be 25x+5x

=30x

present mean age= 30x/x

=30

Hence, present mean age of the family is 30 years