Question

When the speed of the boat in still water is increased by 3 km/h, it travels a distance of 460 km upstream in 23 hours. The speed of the stream is 5 km/h. Find the time the boat will take to travel 460 km downstream when the speed of the boat in still water is decreased by 4 km/h.
1. 22 hours
2. 25 hours
3. 20 hours
4. 27 hours

Answer 1

Correct Answer - Option 3 : 20 hours

Given:

The speed of the boat in still water = increased by 3km/h

The speed of the stream = 5km/h

Distance travelled in 23 hours = 460 km

Formula:

Speed = Distance/Time

Time taken by boat to travel upstream = D/(speed of boat in still water - speed of the stream)

Time taken by boat to travel downstream = D/(speed of boat in still water + speed of the stream)

Calculation:

Let the speed of boat be x km/h

According to the question

23 = 460/[(x + 3) – 5]

⇒ 1 = 20/(x – 2)

⇒ (x - 2) = 20

⇒ x = 22 km/h

Required time = 460/(18 + 5) = 460/23 = 20 hours

∴ The time taken by boat to travel distance is 20 hours.