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document.write( "The speed of a stream is 5 mph. A boat travels 9 miles upstream in the same time it takes to travel 19 miles downstream. What is the speed of the boat in still water?
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document.write( "Let u = the speed of the boat in still water.\r\n" );
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document.write( "Then the speed of the boat relative the bank of the river is u-5 
when it moves upstream, and u+5 when it moves downstream.\r\n" );
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document.write( "We can write the basic equation for travel and distance problems \r\n" );
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document.write( "Time = 
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document.write( "in the form \r\n" );
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document.write( "t = 
(1) for moving upstream, and\r\n" );
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document.write( "t = 
(2) for moving downstream.\r\n" );
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document.write( "Since the left side, t, is the same in both equations, you get a single equation for u\r\n" );
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document.write( " = .\r\n" );
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document.write( "To solve it, multiply both sides by the product (u-5)*(u+5) and simplify:\r\n" );
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document.write( "9*(u+5) = 19*(u-5),\r\n" );
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document.write( "9u + 45 = 19u - 95,\r\n" );
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document.write( "45 + 95 = 19u - 9u,\r\n" );
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document.write( "10u = 140,\r\n" );
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document.write( "u = 
= 14 mph.\r\n" );
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document.write( "It is your answer: the speed of the boat in still water is 14 miles per hour.\r\n" );
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