A boat travels 24 km downstream in 10 hours, but takes 2 hours longer to cover the same distance upstream. What is the boat's speed in still water?

Explanation

The downstream speed is 24 km divided by 10 hours, which equals 2.4 km/hr. The upstream speed is 24 km divided by 12 hours, resulting in 2 km/hr. The boat's speed in still water is the average of these two speeds: (2.4 + 2) / 2 = 2.2 km/hr. Since this value does not match any of the given options, the correct choice is 'None of the above'.