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# How many kids?

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200
2

The average age of a family(two parents and their children) is 20. If we exclude one parent, who is 40, the average age drops to 15.
How many children are there in the family? Thanks for help.

Guest Apr 16, 2017
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#1
+1

Let the number of children =C

Let the sum total of the whole family's ages =S

S/(C+2)=20..........................(1)

(S-40) /(C+1) =15.................(2), solve for C, S

C = 3 children in the family

S =100 - The family combined ages.

Guest Apr 16, 2017
#2
+75352
+1

Let the sum of all ages = A

And let N be the number of family members.......then we have two equations

A  =  20N

A - 40  = 15(N - 1)   →  A  =  15(N-1) + 40

Setting these equal, we have

20N  =   15(N-1) + 40

20N  = 15N + 25

5N  = 25

N  = 5

Thus.....we have  2 adults and 3 children

CPhill  Apr 16, 2017

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