document.write( "Question 1190128: A boat on a river travels downstream between two points, 80 mi apart, in 1 h. The return trip against the current takes 2.5 hours
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Algebra.Com's Answer #821710 by ikleyn(52778) $\"\"$ $\"About$

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\n" ); document.write( "A boat on a river travels downstream between two points, 80 mi apart, in 1 h.
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document.write( "Let  u  be the boat speed in still water (in miles per hour, mph).\r\n" );
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document.write( "Let  v  be the rate of the current, in mph.\r\n" );
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document.write( "Then  the boat's  effective speed downstream is  u+v  mph,\r\n" );
document.write( "while the boat's  effective speed upstream   is  u-v  mph.\r\n" );
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document.write( "Now, \"speed\" equation for boat floating upstream is \r\n" );
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document.write( " = u - v    (1)    (speed upstream = the distance divided by time upstream)\r\n" );
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document.write( "Next, \"speed\" equation for boat floating downstream is \r\n" );
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document.write( " = u + v    (2)    (speed downstream = the distance divided by time  downstream)\r\n" );
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document.write( "Simplify equations (1) and (2)\r\n" );
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document.write( "u - v = 32     (3)\r\n" );
document.write( "u + v = 80     (4)\r\n" );
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document.write( "Now add equations (3) and (4) to eliminate \"v\". You will get\r\n" );
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document.write( "2u = 80 + 32 = 112  ====>  v =  = 56.\r\n" );
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document.write( "ANSWER.  The rate of the boat in still water is 56 miles per hour.    ANSWER\r\n" );
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