The sum of ages of a father and his son is 45 years. Five years ago, the product of their ages was 124. How old is the father now?

Explanation

Let father’s age = F and son’s age = S. F + S = 45. Five years ago: (F – 5)(S – 5) = 124. Since S = 45 – F, (F – 5)(40 – F) = 124 => F^2 – 45F + 324 = 0 => (F – 36)(F – 9) = 0. Father’s age is 36 years.