Correct Answer - Option 3 : 20

Let, age of Son = p

Age of Father = 2p

**Ten years back:**

**Age of father = (2p - 10)**

**Age of son = (p - 10)**

So;

Age of father = 3 × Age of son

(2p - 10) = 3 × (p - 10)

2p - 10 = 3p - 30

3p - 2p = 30 - 10

p = 20

So, age of son = 20 years.

Hence, **"20"** is the correct answer.