Let the present age (in year) of father and his two children be x, y and z year, respectively.
Now by given condition, x = 2(y + z) …(i)
and after 20 year, (x + 20) = (y + 20) + (z + 20)
so, x = y + z + 20 or y + z = x - 20 …(ii)
On putting the value of (y + z) in Eq, (i) and get the present age of father
So, x = 2(x -20)
x = 40
Hence, the father’s age is 40 yr.