Question

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

Answer 1

Let the number of family members be ${}^{\prime }{x}^{\prime }$

The average age of the family members $5$ years ago is $25$ years

So, the sum of age of all family members 5 years ago $=25x$

The sum of age of these family members now ie. after 5 years elapsed

$=25x+$ 5 yea of each family member ie $5x$

$=25x+5x=30x$

Present sum of ages of all the five members $=30x$

Therefore, current, average age $=\frac{\text{sum of ages}}{\text{no. of members}}=\frac{30x}{x}=30$