Multiple choice

After five years, the age of a father will be thrice the age of his son. Five years ago, he was seven times old as his son was. What is father's present age?

  1. $35$ years
  2. $40$ years
  3. $45$ years
  4. $50$ years
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let F and S be present ages. F+5 = 3(S+5) => F+5 = 3S+15 => F = 3S+10. F-5 = 7(S-5) => F-5 = 7S-35 => F = 7S-30. 3S+10 = 7S-30 => 4S = 40 => S = 10. F = 3(10)+10 = 40.

AI explanation

Let the present ages of the father and son be F and S. The given conditions translate to F + 5 = 3(S + 5) and F - 5 = 7(S - 5). Solving the first equation gives F = 3S + 10, and solving the second gives F = 7S - 30. Equating the two expressions for F yields 3S + 10 = 7S - 30, so S = 10. Substituting S = 10 gives F = 40.

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