Question 1004729
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A boat went 8 kilometers upstream and returned all in two hours. If the current was running at 3 km/hr, what is the boat's speed in still water. 
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Let u be the boat's speed in still water in  {{{km/h}}}.

Then the boat's speed relative to the river's bank is  (u-3)  upstream and  (u+3)  downstream.


The time the boat spent for the upstream trip is  {{{8/(u-3)}}} hours.

The time the boat spent for the downstream trip is  {{{8/(u+3)}}} hours.


So, you have an equation for the duration of the close loop trip:


{{{8/(u-3)}}} + {{{8/(u+3)}}} = 2.


Solve it.  The first step is to multiply both sides by  (u-3)*(u+3).


<U>Answer</U>. &nbsp;9 {{{km/h}}}.