The sum of ages a father and son is 45 years. Five years ago, the product of their ages was four times the father’s age at that time. The present age of the father is

A. 39 years
C. 25 years
B. 36 years
D. None of these
Answer : B

Explanation :

Le father’s present age = x years
Then, son’s present age = (45 – x) years
Given: (x – 5)(45 – x – 5) = 4(x – 5)
or, x2 - 41x + 180 = 0 or, (x - 36)(x - 5) = 0
  x = 36 years.