After five years, the age of a father will be thrice the age of his son, whereas five years ago, he was seven times old as his son was. What is father's present age?

Explanation Option [b] is correct. Let the age of son after 5 years be x years. Then, the age of father after 5 years would be 3x years. Five years ago the age of son = (x ? 10) years. Five years ago the age of father = (3x ? 10) years According to the given information in the question, (3x−10)=7(x−10) or      3x−10=7x−70 or      4x=60  or   x=15 years Therefore, present age of father would be (3x ? 5) years or (45 ? 5) = 40 years.