Let the present age (in year) of father and his two children be x, 1 and z yr, respectively now by given condition , x = 2(y + z)
And after 20 yr. (x + 20) = ( y + 20) + (z + 20)
⇒ y + z + 40 = x + 20
⇒ y + z = x - 20
On the putting the value of (y + z) in Eq. (i) and get the present age of father
x = 2(x – 20)
x = 2x – 40 = 40
hence, the father’s age is 40 yr.