Question 1130533
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Note that you can solve the problem informally, using logical reasoning and some simple calculations, instead of using the formal algebraic approach shown by tutor @ikleyn.  The formal algebraic method is certainly valid; but if you just need to solve the problem quickly by whatever method you want (as in a timed mathematics competition), then this alternative method is very useful.<br>
Simple calculations show that the speed of the boat with the current is 35mph while its speed against the current is 15mph.<br>
The 35mph is the boat's speed PLUS the speed of the current; the 15mph is the boat's speed MINUS the speed of the current.  Common sense then says that the speed of the boat is halfway between 15mph and 35mph: 25mph.  And then the speed of the current is the difference between 25mph and either 15mph or 35mph.<br>
So the speed of the boat is 25mph and the speed of the current is 10mph.