SOLUTION: A father is at present three times old as his son five year back he was four times as old as his son find the age of his son

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Question 774951: A father is at present three times old as his son five year back he was four times as old as his son find the age of his son
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +f+ = father's age now
Let +s+ = son's age now
-----------------------
(1) +f+=+3s+
(2) +f+-+5+=+4%2A%28+s+-+5+%29+
----------------------
Substitute (1) into (2)
(2) +3s+-+5+=+4%2A%28+s+-+5+%29+
(2) +3s+-+5+=+4s+-+20+
(2) +s+=+20+-+5+
(2) +s+=+15+
The son is 15
check:
(1) +f+=+3%2A15+
(1) +f+=+45+
and
(2) +f+-+5+=+4%2A%28+s+-+5+%29+
(2) +45+-+5+=+4%2A%28+15+-+5+%29+
(2) +40+=+5%2A10+
(2) +40+=+40+
OK