Question

a father is twice as old as his son 10 years ago the father was thrice as old as his son find their present age

Answer 1

Let the father's age be 'x' and
      his son's age be 'y'.
PRESENT:
The father is twice as old as his son.
        ∴x=2y→1
PAST:
10 years ago, the father was thrice as old as his son.
∴x-10=3(y-10)
  x-10=3y-30
  x-3y=-30+10
  x-3y=-20
Substituting this in 1, we get:
   2y-3y=-20
         -y=-20
        ∴y=20.
Substituting this in 1, we get:
        x=2y
          =2(20)
      ∴x=40.
∴The present age of father is 40 years and his son's age is 20 years.