A person can row a boat at 5 km/hr in still water. If the speed of water current in a river is 1 km/hr, and it takes him 1 hour to row to a place and come back, how far off is the place?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 2.4 km
The downstream speed is 5 + 1 = 6 km/hr and the upstream speed is 5 − 1 = 4 km/hr. Let the place be d km away. The total time is 1 hour:
\( \displaystyle \frac{d}{6} + \frac{d}{4} = 1 \)
\( \displaystyle \frac{2d + 3d}{12} = 1 \)
\( \displaystyle d = \frac{12}{5} = 2.4 \) km