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A man can row his boat at speed of 3 km/h and he finds that the time taken rowing upstream is twice the time taken downstream. Find the speed of the stream?


1. 2 km/h
2. 1 km/h
3. 3 km/h
4. 4 km/h
5. None of these

1 Answer

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Best answer
Correct Answer - Option 2 : 1 km/h

Given:

Speed of boat = x km/h = 3 km/h

Time taken upstream = 2t

Time taken downstream = t

Formula:

Speed of downstream = Speed of a boat in still water + Speed of water current

Speed of upstream = Speed of a boat in still water + Speed of water current

Speed = Distance/Time

Concept:

Distance is constant

Calculation:

Let the speed of the boat in still water be x km/h and speed of water current be y km/h

Speed of downstream = x + y

⇒ (3 + y)

Speed of upstream = x – y

⇒ (3 – y)

Now,

By using the concept of distance is constant

Distance = (3 + y) × t    ……. (1)

Distance = (3 – y) × 2t   ……. (2)

Now,

Equate the equation (1) and (2) then we get

(3 + y) × t = (3 – y) × 2t

⇒ (3 + y) = (3 – y) × 2

⇒ 3 + y = 6 – 2y

⇒ 3 – 6 = – 3y

⇒ – 3 = – 3y

⇒ 3 = 3y

⇒ y = 3/3

⇒ y = 1 km/h

The Speed of the stream is 1 km/h 

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