Multiple choice general knowledge math & puzzles

Speed of a boat in standing water is 9 kmph and the speed of the stream is 1.5 kmph. A man rows to a place at a distance of 105 km and comes back to the starting point. The total time taken by him is:

  1. 16 hours

  2. 18 hours

  3. 20 hours

  4. 24 hours

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

Downstream speed = 9 + 1.5 = 10.5 kmph. Upstream speed = 9 - 1.5 = 7.5 kmph. Time taken = (105 / 10.5) + (105 / 7.5) = 10 + 14 = 24 hours. Other options are mathematically inconsistent with the provided speeds and distance.