Let's denote the present age of the son as \( S \) years. According to the information given, the present age of the father is \( 2S + 10 \) years.
We want to find out in how many years, say \( x \), the age of the father will be twice the age of the son. In \( x \) years, the father's age will be \( 2S + 10 + x \) and the son's age will be \( S + x \).
We set up the equation based on the condition that the father's age will be twice the son's age:
\[ 2S + 10 + x = 2(S + x) \]
Now, expanding the right-hand side of the equation gives:
\[ 2S + 10 + x = 2S + 2x \]
Next, we can simplify this equation by subtracting \( 2S \) from both sides:
\[ 10 + x = 2x \]
Now, rearranging the equation gives:
\[ 10 = 2x - x \] \[ 10 = x \]
Thus, in \( 10 \) years, the father's age will be twice the son's age.