A streamer goes downstream from one port to another in 4

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A streamer goes downstream from one port to another in 4 h. It covers the same distance upstream in 5 h. If the speed of the stream is 2 km/h , find the distance between the two ports ?

1. 50 km/h
2. 60 km/h
3. 70 km/h
4. 80 km/h

Correct Option: D

Let the distance between the two ports = L km
Then, speed downstream = L/4
and speed upstream = L/5
∴ Speed of the stream = 1/2(L/4 - L/5)
⇒ 1/2[(5L - 4L)/20] = 2
⇒ L = 80 km