SOLUTION: the average of 5 members family age is 18 years . if grandfather is included the average is 12 years. what is the age of grandfather?

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Question 764320: the average of 5 members family age is 18 years . if grandfather is included the average is 12 years. what is the age of grandfather?
Answer by josgarithmetic(39618) About Me  (Show Source):
You can put this solution on YOUR website!
%285%2A18%2Bg%29%2F6=12, find g.

Why would a grandfather, of expected age ABOVE 30, make a decrease of the average age for the group when the average age without grandfather is already younger? The problem description just makes no realistic sense.

%285%2A18%2Bg%29%2F6=12
5%2A18%2Bg=6%2A12
g=6%2A12-5%2A18=2%2A3%2A2%2A2%2A3-5%2A2%2A3%2A3=2%2A2%2A2%2A3%2A3-2%2A3%2A3%2A5
g=2%2A3%2A3%284-5%29%3C0
The problem description is wrong.