SOLUTION: A boat sails upstream and after 2 hours it has sailed 10km. if the boat would sail downstream, it would sail 30 km in 2 hours calculate the speed of the boat and of the stream in k

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Question 1084421: A boat sails upstream and after 2 hours it has sailed 10km. if the boat would sail downstream, it would sail 30 km in 2 hours calculate the speed of the boat and of the stream in km/h
Answer by ikleyn(52786) About Me  (Show Source):
You can put this solution on YOUR website!
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The effective speed upstream is 10%2F2 = 5 km/h.
It is the difference of the boat speed in still water "u" and the rate of stream "v":

u - v =  5.    (1)


The effective speed downstream is 30%2F2 = 15 km/h.
It is the sum of the boat speed in still water "u" and the rate of stream "v":

u + v = 15.    (2)


Add the equations (1) and (2). You will get

2u = 5 + 15 = 20,   --->  u = 20%2F2 = 10 km/h.


Thus the speed of the boat in still water is 10 km/h.

Then the speed of the stream is v = 15 - 5 = 15 - 10 = 5 km/h, from equation (2).


Answer.  The speed of the boat in still water is 10 km/h.  The speed of the stream is 5 km/h.