Multiple choice

Find the time taken by Aman when he uses a boat to cover a distance of 28 km upstream. The ratio of the speed of boat in still water to the speed of stream is 9 : 3. It is also given that the same boat covers a distance of 20 km downstream in 50 minutes.

  1. 2 hours 10 minutes

  2. 2 hours 20 minutes

  3. 2 hours 15 minutes

  4. 1 hour 55 minutes

  5. 2 hours 55 minutes
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Downstream speed = 20 km / (50/60) hr = 24 km/hr. Ratio of boat (B) to stream (S) is 9:3, so B=3S. Downstream speed = B + S = 4S = 24, so S = 6 and B = 18. Upstream speed = B - S = 18 - 6 = 12 km/hr. Time = 28 / 12 = 2.33 hours = 2 hours 20 minutes.

AI explanation

First, find the actual downstream speed using Speed = Distance / Time, which gives 20 / (50/60) = 24 km/hr. Since the ratio of the boat's speed to the stream's speed is 9 : 3, the downstream speed consists of 12 ratio parts, meaning one ratio part equals 24 / 12 = 2 km/hr. The upstream speed will have 9 - 3 = 6 ratio parts, making it 6 * 2 = 12 km/hr. Using Time = Distance / Speed, the time to cover 28 km upstream is 28 / 12 hours, which equals 2 hours and 20 minutes.

Keep practicing — related questions