The grandfather is three years older than an grandmother. The average age of the grandmother, the grandfather and their seven grandchildren is 28 years. The grandchildren have a total of 105 years. Calculate how old is grandfather.


o =  75


o = m + 3
(m+o+7*v)/(1+1+7) = 28
v = 105/7

m-o = -3
0.111111m+0.111111o+0.777778v = 28
7v = 105

m = 72
o = 75
v = 15

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