document.write( "Question 419040: The current of a river is 2 miles per hour. A boat travels to a point 8 miles upstream and back again in 3 hours.
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Algebra.Com's Answer #853230 by ikleyn(53427) $\"\"$ $\"About$

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\n" ); document.write( "The current of a river is 2 miles per hour. A boat travels to a point 8 miles upstream and back again in 3 hours.
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\n" ); document.write( "\n" ); document.write( " The solution and the answer in the post by @mananth both are incorrect.\r
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document.write( "speed in still water =  x mph.			\r\n" );
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document.write( "current speed 		2 mph.		\r\n" );
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document.write( "upstream speed   = x-2 mph.		\r\n" );
document.write( "downstream speed = x+2 mph.			\r\n" );
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document.write( "Distance = 	8 miles.			\r\n" );
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document.write( "Time equation\r\n" );
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document.write( "     +  = 3				.\r\n" );
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document.write( "    LCD = (x-2)*(x+2)								\r\n" );
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document.write( "    8*(x-2) + 8*(x+2) = 3				\r\n" );
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document.write( "    8x - 16+ 8x + 16 = 3(x^2-4)\r\n" );
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document.write( "    16x = 3x^2 - 12						\r\n" );
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document.write( "    3x^2 - 16x - 12=0	\r\n" );
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document.write( "Use the quadratic formula \r\n" );
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document.write( "    b^2 - 4ac = (-16)^2 - 4*3*(-12) = 256 + 144 = 400\r\n" );
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document.write( "    x = 				\r\n" );
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document.write( "Use positive root  =  = 6.\r\n" );
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document.write( "ANSWER.  The speed of the boat in still water is 6 mph.\r\n" );
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