Multiple choice general knowledge math & puzzles

A fathers age today is thrice as that of his sons. After 5 years, it would be just 2.5 times. At the time of birth of his son, what must be the age of the father?

  1. 30yrs

  2. 25yrs

  3. 28yrs

  4. 35yrs

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let the son's current age be x years. Then the father's current age is 3x years. After 5 years: (3x + 5) = 2.5(x + 5), which gives 3x + 5 = 2.5x + 12.5, so 0.5x = 7.5 and x = 15. The son is 15 years old now, and the father is 45 years old now. At the son's birth (15 years ago), the father's age was 45 - 15 = 30 years.