document.write( "Question 1167838: Peter can row 11 miles downstream in the same time it takes him to row 7 miles upstream. He rows downstream for 3 hours, then turns and rows back for 4 hours, but finds he is still 5 miles from where he started his trip. What is the speed of the current? \n" ); document.write( "
Algebra.Com's Answer #792452 by Edwin McCravy(20056)\"\" \"About 
You can put this solution on YOUR website!
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document.write( "He's right but I think I'd do it this way:\r\n" );
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document.write( "Let t be that same time that it takes him to go 11 miles upstream\r\n" );
document.write( "that it takes him to go downstream 7 miles.  So make this chart \r\n" );
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document.write( "                       distance   rate    time\r\n" );
document.write( "downstream 1st time       11               t  \r\n" );
document.write( "upstream 1st time          7               t\r\n" );
document.write( "downstream 2nd time                        3  \r\n" );
document.write( "upstream 2nd time                          4\r\n" );
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document.write( "Use rate = distance/time to fill in the rates\r\n" );
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document.write( "                       distance   rate    time\r\n" );
document.write( "downstream 1st time       11      11/t     t  \r\n" );
document.write( "upstream 1st time          7       7/t     t\r\n" );
document.write( "downstream 2nd time               11/t     3  \r\n" );
document.write( "upstream 2nd time                  7/t     4\r\n" );
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document.write( "Use distance = rate x times to fill in the other two distances:\r\n" );
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document.write( "                       distance   rate    time\r\n" );
document.write( "downstream 1st time       11      11/t     t  \r\n" );
document.write( "upstream 1st time          7       7/t     t\r\n" );
document.write( "downstream 2nd time      33/t     11/t     3  \r\n" );
document.write( "upstream 2nd time        28/t      7/t     4 \r\n" );
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document.write( "So the two distances are 5 miles apart, so\r\n" );
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document.write( "33/t - 28/t = 5\r\n" );
document.write( "        5/t = 5\r\n" );
document.write( "          5 = 5t\r\n" );
document.write( "          1 = t\r\n" );
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document.write( "So his rate upstream is 11/1 = 11 mph and his rate downstream is 7/1 = 7 mph\r\n" );
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document.write( "The average of those is 9 mph, his speed in still water.  So the speed of\r\n" );
document.write( "the current is how much the current speeds him up going with it, and how much\r\n" );
document.write( "it slows him down going against it, which is 2 mph.\r\n" );
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document.write( "Edwin
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