If the present age of father is years and that of his son is years, then
(Age of father after years) : ( Age of son years ago)________
Given that,
Present age of father
Present age of son
Age of father after years
Age of son years ago
Now, ratio of age of father after years to the age of son years ago
Lowest form of (Divide both and by their HCF )
Hence, (Age of father after years) : ( Age of son years ago)