Question

Five years from now a father's age will be three times his son's age and 5 years ago he was seven times as old as his son was. what are their present ages?

Answer 1

Let's say the son is x years old now, 
In five years time, he will be (x+5) years old
The father's age in five years time is 3(x+5)
The son's age five years ago was x-5
The father's age five years ago was 7(x-5)
Five years ago and five years from now are 10 years apart. This means that the father's age five years from now is 10 years more than his age five years ago
7(x-5)+10=3(x+5)
7x-35+10=3x+15
7x-3x=15-10+35
4x=40
x=10
The boy is currently 10 years old
The father will be 3(x+5) in five years time=45
So the father is currently 40 years old