A boat leaves it's dock and travels upstream at a speed of 40 km/hr and then returns to the dock. What is the speed of the stream if they average speed of the entire trip is 60 km/hr?

20 km/hr

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30 km/hr

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50 km/hr

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none of these

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Solution

The correct option is D
none of these

Speed of stream = x.
Speed of boat = b.
Given, b - x = 40.
Also,

$\frac{2 [(b + x) (b - x)]}{(b + x + b - x)} = 60 \Rightarrow \frac{2 (b + x) (40)}{2 b} = 60.$

Solving we get b= 2x.
2x - x = 40 , x = 40 (d).

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A boat leaves it's dock and travels upstream at a speed of 40 km/hr and then returns to the dock. What is the speed of the stream if they average speed of the entire trip is 60 km/hr?

The correct option is D none of these Speed of stream = x. Speed of boat = b. Given, b - x = 40. Also, 2[(b+x)(b−x)](b+x+b−x)=60⇒2(b+x)(40)2b=60. Solving we get b= 2x. 2x - x = 40 , x = 40 (d).

The correct option is D
none of these

Speed of stream = x.
Speed of boat = b.
Given, b - x = 40.
Also,

$\frac{2 [(b + x) (b - x)]}{(b + x + b - x)} = 60 \Rightarrow \frac{2 (b + x) (40)}{2 b} = 60.$

Solving we get b= 2x.
2x - x = 40 , x = 40 (d).