Question 187888
let x= present dad age; y=present son age
establis the equation as follows:
x-20=y .........(1)
x+5=3(y+5) .....(2)

take (1) subtract from (2) we have:
x+5-x+20 = 3y+15-y
        2y= 25-15
        2y = 10
         y = 5
Present son age is 5 years old and Dad present age is x= x+20=5+20
                                                      x= 25 years old