The sum of the ages of a father and son is 45 years. Five year ago the product to their ages was four times the father's age that time. The present age of the father and son respectively are?

Let the father's age be F and the son's age be S. We know F + S = 45. Five years ago, their ages were (F-5) and (S-5). The product was four times the father's age: (F-5)(S-5) = 4(F-5). Assuming F ≠ 5, we can divide: S-5 = 4, so S = 9. Then F = 45 - 9 = 36. Checking: 5 years ago, ages were 31 and 4, product is 124, which is indeed 4*31 = 124. Present ages are 36 and 9.