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A boat makes a round trip of 240 km in 13 hours when the speed of the stream is 14 km/hour. What is the downstream speed in km/hr?
1. 40
2. 35
3. 55
4. 50

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Correct Answer - Option 1 : 40

Given:

A boat makes a round trip of 240 km in 13 hours when the speed of the stream is 14 km/hour

Formula:

Upstream = (u − v) km/hr

where “u” is the speed of the boat in still water

“v” is the speed of the stream

Downstream = (u + v) Km/hr

where “u” is the speed of the boat in still water

“v” is the speed of the stream

Speed of Boat in Still Water = (1/2)(Downstream Speed + Upstream Speed)

Speed of Stream = (1/2)(Downstream Speed – Upstream Speed)

Calculation:

Let the speed of the boat in still water be x km/hr

Upstream Speed = x - 14

Downstream Speed = x + 14

{120/(x - 14)} + {120/(x + 14)} = 13

⇒ x = 26

Downstream speed = x + 14 = 40 km/h

∴ The downstream speed is 40 km/h.

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