Final answer:
By setting up an equation based on the given relationship between the son's and father's ages, we find out the son is currently 10 years old and will be 15 years old in 5 years.
Step-by-step explanation:
Let's assume the current age of the son is x years, and the age of the father is 4x years. In 20 years, the son will be x + 20 years old, and the father will be 4x + 20 years old. According to the problem, at that time, the father's age will be twice the son's age, so we can set up the following equation:
4x + 20 = 2(x + 20).
Solving this equation gives us:
4x + 20 = 2x + 40
→ 4x - 2x = 40 - 20
→ 2x = 20
→ x = 10.
This means the son is currently 10 years old. To find out the son's age in 5 years, we simply add 5 to his current age:
10 + 5 = 15 years old.
The son will be 15 years old in 5 years.