document.write( "Question 1187389: A jet liner flying east with the wind traveled 4200 km in 7 hours. The return trip, flying against the wind, took 10 hours. Find the rate at which the jet flew in still air and the rate of the wind. \n" ); document.write( "

Algebra.Com's Answer #818357 by ikleyn(52866) $\"\"$ $\"About$

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\n" ); document.write( "A jet liner flying east with the wind traveled 4200 km in 7 hours.
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\n" ); document.write( "Find the rate at which the jet flew in still air and the rate of the wind.
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document.write( "From the condition you have these two equations\r\n" );
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document.write( "  = u + v,   (1)\r\n" );
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document.write( "  = u - v.   (2)\r\n" );
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document.write( "The left side of the equation (1) is the speed of the plane relative the ground when flying with the wind, \r\n" );
document.write( "and it is the sum of the rate of the plane in still air \"u\" and the wind's rate \"v\".\r\n" );
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document.write( "The left side of the equation (2) is the speed of the plane relative the ground when flying against the wind, \r\n" );
document.write( "and it is the difference of the rate of the plane in still air \"u\" and the wind's rate \"v\".\r\n" );
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document.write( "Simplify the equations (1) and (2):\r\n" );
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document.write( "u + v = 600,    (3)\r\n" );
document.write( "u - v = 420     (4)\r\n" );
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document.write( "Now add the equations (3) and (4). You will get\r\n" );
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document.write( "2u = 600 + 420 = 1020,  or  u = 1020/2 = 510.\r\n" );
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document.write( "Thus you just found the speed of the plane in still air. It is 510 miles per hour.\r\n" );
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document.write( "Now it is easy to find the speed of the wind. It is\r\n" );
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document.write( "v = 600 - 510 = 90  miles per hour.\r\n" );
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document.write( "ANSWER.  The speed of the plane in still air is 510 mph.  The speed of wind is 90 mph.\r\n" );
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