Multiple choice

The sum of ages of a father and son is $45$ years. Five years ago the product of their ages was $4$ times the age of the father at that time. The present age of the father is

  1. $30$ yrs
  2. $31$ yrs
  3. $36$ yrs
  4. $41$ yrs
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let father's age be F and son's be S. F + S = 45. Five years ago, (F-5)(S-5) = 4(F-5). Since F is not 5, we divide by (F-5) to get S-5 = 4, so S = 9. Then F = 45 - 9 = 36.

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