A person rows at a speed of 9 km/h in still water. He takes 4.5 hours to travel from point A to point B and back again. If the current flows at 1 km/h, what is the distance between points A and B?

Explanation

Let the distance between A and B be x km. The time taken to row downstream is x/(9 + 1) = x/10 hours, and upstream is x/(9 - 1) = x/8 hours. The total time is given as 4.5 hours, so: x/10 + x/8 = 4.5. Multiplying both sides by 40 gives 4x + 5x = 180, which simplifies to 9x = 180. Therefore, x = 20 km. Since 20 km is not listed among the options, the correct choice is 'None of the above'.