document.write( "Question 1124064: Alonzos boat has a top speed of 20 miles per hour in still water. While traveling on a river at top speed, he went 40 miles upstream in the same amount of time he went 60 miles downstream. Find the rate of the river current. \n" ); document.write( "

Algebra.Com's Answer #740433 by ikleyn(52778) $\"\"$ $\"About$

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document.write( "Let x = the rate of the river current, in miles per hour.\r\n" );
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document.write( "Then the effective rate downstream is  (20+x) mph, \r\n" );
document.write( "while the effective rate upstream  is  (20-x) mph.\r\n" );
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document.write( "The time traveling 40 miles upstream   is  .\r\n" );
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document.write( "The time traveling 60 miles downstream is  .\r\n" );
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document.write( "The times are equal, so you have an equation\r\n" );
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document.write( "     = .\r\n" );
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document.write( "To solve it, multiply both sides by  20-x)*(20+x). You will get\r\n" );
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document.write( "    40*(20+x) = 60*(20-x),\r\n" );
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document.write( "    800 + 40x = 1200 - 60x\r\n" );
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document.write( "    40x + 60x = 1200 - 800\r\n" );
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document.write( "    100x = 400   ======>  x = 400/100 = 4.\r\n" );
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document.write( "Answer.  The rate of the river current is 4 miles per hour.\r\n" );
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