SOLUTION: Five years ago, a father was seven times as old as his son. Five years hence, the father will be three times as old as his son. Find their own and present ages.

Question 1005425: Five years ago, a father was seven times as old as his son. Five years hence, the father will be three times as old as his son. Find their own and present ages.
Answer by fractalier(6550) (Show Source): You can put this solution on YOUR website!
Call their ages NOW, f and s. Then we have
f - 5 = 7(s - 5) and
f + 5 = 3(s + 5)
Solve the first one for f and substitute that into the second equation...
f = 7(s - 5) + 5 = 7s - 35 + 5 = 7s - 30
and now substituting
7s - 30 + 5 = 3(s + 5)
7s - 25 = 3s + 15
4s - 25 = 15
4s = 40
s = 10
f is then 40.
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