Question

How many kids?
There is a happy family consisting of 2 parents and kids. The average age of the family is 20. But if we exclude one parent whose age is 40, the average age of the family drops to 15. Find the number of kids in the family.

Answer 1

Let the number of kids in the family be x.

Let the sum of 2 parents and their kids be y.

Given that Average age of the family is 20.

y/x + 2 = 20

y = 20(x + 2)   ---- (1).

if we exclude one parentage is 40, the average age of the family drops to 15.

y - 40/x + 1 = 15.

y = 15(x+1) + 40

   = 15x + 55   ---- (2).


On solving (1) and (2), we get

20(x + 2)  = 15x + 55

20x + 40 = 15x + 55

5x - 15 = 0

x = 3.

The number of kids in the family = 3.


Hope this helps!