Multiple choice

A father and his son start at a point A with spends of $12$ kmph and $18$ kmph respectively, and reach another point B. If his son starts $60$ minutes after his father at A and reaches B $60$ minutes before his father, what is the distance between A and B?

  1. $90\ km$
  2. $72\ km$
  3. $36\ km$

  4. None of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

If the distance is D, the father's travel time is D/12 and the son's is D/18. Because the son starts 1 hour later and arrives 1 hour earlier, D/12 = D/18 + 2, which gives D = 72 km.

AI explanation

Let the distance between A and B be D km. The father takes D/12 hours and the son takes D/18 hours to complete the journey. The total time difference between their travels is the 60 minutes the son waits plus the 60 minutes he arrives early, totaling 2 hours, so D/12 minus D/18 equals 2. Solving this gives (3D minus 2D) divided by 36 equals 2, meaning D equals 72 km.

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