When the father was 24 years, the son was 0 year.
Fathers age now will be addition of the son's age to 24 years. Thus when the son is 1 year, the father is 25 year
(24+1), when the son is 2 years, the father is 26 years
(24+2), etc.
Let
x= son's age now.
When the son is
x years, the father is
24+x years
Now he is three times as old as his son means when you multiply the son's age now by 3, you will get the father's age.
3×x= father's age now But the father's age is also
24+x years now hence we can equate the two expressions and solve for the value of
x.
3xx=24+x3x=24+x3x−x=242x=24Divide both sides of the equation by 2
x==12The son is 12 years now.