A boat travels in still water at a speed of 9 km/h, while the current flows at 1.5 km/h. If a man rows to a destination 105 km away and then returns to his starting point, how long does the entire journey take?

Explanation

The boat's effective speed downstream is 9 + 1.5 = 10.5 km/h, and upstream speed is 9 - 1.5 = 7.5 km/h. Time taken downstream = 105 / 10.5 = 10 hours. Time taken upstream = 105 / 7.5 = 14 hours. Total time = 10 + 14 = 24 hours.