document.write( "Question 428014: A plane flies 435 miles with the wind and 345 miles against the wind in the same length of time. If the speed of the wind is 15mph, find the speed of the plane in still air. \n" ); document.write( "

Algebra.Com's Answer #853193 by ikleyn(53422) $\"\"$ $\"About$

You can put this solution on YOUR website!
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\n" ); document.write( "A plane flies 435 miles with the wind and 345 miles against the wind in the same length of time.
\n" ); document.write( "If the speed of the wind is 15 mph, find the speed of the plane in still air.
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\n" ); document.write( "\n" ); document.write( " The solution in the post by @manath is incorrect.\r
\n" ); document.write( "\n" ); document.write( " I came to bring a correct solution.\r
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document.write( "let speed in still air be x mph\r\n" );
document.write( "wind speed 15 mph  (given).\r\n" );
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document.write( "against wind x - 15 mph\r\n" );
document.write( "with    wind x + 15 mph\r\n" );
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document.write( "Distance against   wind 345\r\n" );
document.write( "Distance with tail wind 435\r\n" );
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document.write( "    Write the \"time\" equation\r\n" );
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document.write( "345 /(x- 15) = 435 /(x+15)    (1)\r\n" );
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document.write( "345 *(x+ 15) = 435 *(x- 15)\r\n" );
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document.write( "345 x + 345*15 = 435 x - 435*15\r\n" );
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document.write( "345*15 + 435*15 = 435x - 345x\r\n" );
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document.write( "11700 = 90x\r\n" );
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document.write( "x = 11700/90 = 130 mph.\r\n" );
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document.write( "ANSWER.  The speed of the plane in still air is 130 mph.\r\n" );
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document.write( "CHECK.  Let's check time (equation (1)):  345/115 = 3 hours;  435/145 = 3 hours.  ! correct !\r\n" );
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\n" ); document.write( "\n" ); document.write( "Solved correctly.\r
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