Q5 of 33 Page 156

Five years ago mean age of a family was 25 years. What is the present mean age of the family?

Let the no of members in family be 'n'.

Mean age = 25


Let x1, x2, …, xn be ages of family members.


We know,


Arithmetic mean of x1, x2, x3, …, xn (n observations) is



Therefore, 5 years ago


⇒ mean age,



⇒ x1 + x2 + …+ xn = 25n [1]


In present, age of each family member will be increase by 5, therefore ages will be


x1 + 5, x2 + 5, …, xn + 5


⇒ Present mean age,



[From 1]



Hence, Present mean age is 30.


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