Question 128

A person can row a distance of one km upstream in ten minutes and downstream in four minutes. What is the speed of the stream ?

Solution

Let the speed of the person be $$x$$ km/h and speed of stream be $$y$$ km/h

=> Speed when going upstream = $$(x - y)$$ km/h

and speed while going downstream = $$(x + y)$$ km/h

=> $$\frac{1}{x - y} = \frac{10}{60}$$

=> $$x - y = 6$$

Also, $$\frac{1}{x + y} = \frac{4}{60}$$

=> $$x + y = 15$$

Subtracting the two equations, we get :

$$2y = 9$$

=> Speed of stream = $$y = 4.5$$ km/h

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