Question

The speed of a boat is 6 km/hr and speed of stream is 2 km/hr. If the boat is running upstream, it takes 4 hours to cover certain distance. How much time it will require to cover the same distance running downstream? 
1. 4 hours
2. 3 hours
3. 2 hours
4. 1 hours

Answer 1

Correct Answer - Option 3 : 2 hours

Given:

Speed of boat = 6 km/hr

Speed of stream = 2 km/hr

It can cover certain distance in upstream in 4 hours

Formula:

Let a = speed of boat and b = speed of strem

Downstream speed = a + b

Upstream speed = a - b

Calculation:

Upstream speed = 6 - 2 = 4 km/hr

Downstream speed = 6 + 2 = 8 km/hr

Distance traveled in upstream = 4 × 4 = 16 km

Distance traveled downstream = 16 km

Time taken to travel 16km downstream = 16/8 = 2 hours

∴ Required time in downstream is 2 hours.