Ravi's speed of rowing in still water is 6 km/hr. He rows between two points in a river and returns to the same starting point. He took 30 minutes more to cover the distance upstream than downstream. If the speed of the stream is 3 km/hr, then the distance between the two points is:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 2.25 km
The downstream speed is the boat speed plus the stream speed, and the upstream speed is the difference:
\(\text{Downstream} = 6 + 3 = 9\) km/hr
\(\text{Upstream} = 6 - 3 = 3\) km/hr
Let the distance be d km. The upstream trip takes 30 minutes \(= \frac{1}{2}\) hour more:
\( \displaystyle \frac{d}{3} - \frac{d}{9} = \frac{1}{2} \)
\( \displaystyle \frac{2d}{9} = \frac{1}{2} \)
\( \displaystyle d = \frac{9}{4} = 2.25 \) km