SOLUTION: The average age of a grandmother, a grandfather, and 7 grandchildren is 28. The average age of 7 grandchildren is 15 years. How old is the grandfather, if he is 3 years older than

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Question 935623: The average age of a grandmother, a grandfather, and 7 grandchildren is 28. The average age of 7 grandchildren is 15 years. How old is the grandfather, if he is 3 years older than the grandmother?
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
1.%28GM%2BGP%2BGK%29%2F9=28
2.GK%2F7=15
3.GP=GM%2B3
From eq. 2,
GK=105
Substitute this and eq. 3 into eq. 1,
%28GM%2BGM%2B3%2B105%29%2F9=28
2GM%2B108=252
2GM=144
GM=72
So then,
GP=72%2B3
GP=75