document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=428014>Question 428014</A>: <I><SPAN STYLE=\"word-break: break-all;\"> 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. </SPAN>\n" );
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document.write( "An informal solution using logical reasoning instead of formal algebra....<br><BR>\n" );
document.write( "The speed with the wind is 15mph greater than the speed of the plane in still air; the speed against the wind is 15mph less than the speed of the plane in still air.  So the difference between the speed with the wind and the speed against the wind is 30mph.<br><BR>\n" );
document.write( "The difference in the distances at the two speeds (in equal amounts of time) is 435-345 = 90 miles; so the time at each speed is 90/30 = 3 hours.<br><BR>\n" );
document.write( "So the speed with the wind is 435/3 = 145mph and the speed against the wind is 345/3 = 115mph.<br><BR>\n" );
document.write( "Then you have three choices for finding the speed of the plane in still air:<BR>\n" );
document.write( "(1) 115+15 = 130mph<BR>\n" );
document.write( "(2) 145-15 = 130mph<BR>\n" );
document.write( "(3) halfway between 115mph and 145mph = 130mph<br><BR>\n" );
document.write( "ANSWER: 130mph<br><BR>\n" );
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document.write( "(Note that the numbers you need to work with are \"nicer\" than those needed in either of the formal algebraic solutions....)<br><BR>\n" );
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