document.write( "Question 1190091: 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. How fast does the current in the river flow? \n" ); document.write( "

Algebra.Com's Answer #821654 by ikleyn(52781) $\"\"$ $\"About$

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\n" ); document.write( "A boat on a river travels downstream between two points, 80 mi apart, in 1 h.
\n" ); document.write( "The return trip against the current takes 2.5 hours.
\n" ); document.write( "How fast does the current in the river flow?
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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 subtract equations (3) and (4) to eliminate \"u\". You will get\r\n" );
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document.write( "2v = 80 - 32 = 48  ====>  v =  = 24.\r\n" );
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document.write( "ANSWER.  The rate of the current is 24 miles per hour.    ANSWER\r\n" );
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\n" ); document.write( "\n" ); document.write( "If you ask me, whether this rate of the current is realistic for such situations, I would answer \"NO\".\r
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