Question

the present age of the father is four times that of his son . 20 years hence the age of father will be twice the age of the son . find their present ages​

Answer 1

The system of equations will be:

F = 4S and

F + 20 = 2(S + 20) which becomes F = 2S + 20

So by substitution, 2S + 20 = 4S, which easily solves to S = 10 (the son’s age now). And by substitution F = 4S = 40 (the father’s age now).

20 years hence, the father will be 60 and the son will be 30.