The age of the father is twice the sum of the ages of his two children. After 20 years, his age will be equal to the sum of the ages of his children. Find the age of the father.

Let the father's age be x years and the sum of ages of 2 children be y years.
As per the question,
x=2y.....(1)
After 20 years,
x+20=y+20+20
$\Rightarrow$ x+20=y+40
$\Rightarrow$ x=y+20.....(2)
Equating (1) & (2),
y = 20
Substituting y = 20 in equation (1), we get
x = 40
Hence, the father's age is 40 years.