Question

Mona's father is thrice as old as Mona. After 12 years, his age will be twice that of his daughter. Find their present age.

Answer 1

let the age of mona be x
so, father age = y
By the problem 
(I) 3x =y      (Present)
(II) 2(x+12) =  y+12     (After 12 yrs)
so from the above two equation we can get
 x=12 and y=36

Answer 2

Let age of Mona be x.

Father's age =3x

According to the question,

The required equation is

3x+12=2x

or, 3x-2x=12

or, x =12

Therefore,Age of Mona is 12 years.

Age of her father is (12×3)=36years

Hope it helps