Correct Answer - Option 2 : 50 years
Let the father's present age be X years.
Father's age 15 years ago = (X - 15) years
Gautam's present age = 20% of (X - 15) = \({\\{(X - 15)} \over 5}\) years
Gaurav's present age = 60% of (X - 10) = \({\\{3(X - 10)} \over 5}\) years
\({\\{(X - 15)} \over 5}\) + \({\\{3(X - 10)} \over 5}\) = 31
X - 15 + 3X - 30 = 155
4X - 45 = 155
4X = 200
X = 50 years
Fatehr's present age is 50 years.
Hence, "option 2" is the correct answer.