document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=579987>Question 579987</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A train went 400 miles from city A to city B at a speed of 80 mph . At what speed should it travel on the way back if wants to have an average speed of 96 mph for the entire round-trip journey ?\r<BR>\n" );
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document.write( "I got answer 112.\r<BR>\n" );
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document.write( "x = 2nd speed.\r<BR>\n" );
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document.write( "(80+x)/2=96\r<BR>\n" );
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document.write( "x = 112\r<BR>\n" );
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document.write( "but some say it should be 120. How?\r<BR>\n" );
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document.write( "Thanks.<BR>\n" );
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document.write( "Entire round trip journey = 800 miles\r<BR>\n" );
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document.write( "solve for time:\r<BR>\n" );
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document.write( "t = 800 / 96 mph = 8 1/3 hours needs to be total time\r<BR>\n" );
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document.write( "already used:\r<BR>\n" );
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document.write( "t = 400 / 80 = 5 hours\r<BR>\n" );
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document.write( "3 1/3 hours left to go 400 miles back, solve for speed:\r<BR>\n" );
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document.write( "v = 400 / (3 1/3) = 120 mph\r<BR>\n" );
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document.write( "its not a simple average, since the train spends different times at each speed\r<BR>\n" );
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document.write( "CHECK:\r<BR>\n" );
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document.write( "800 miles, total time 8 1/3 hours \r<BR>\n" );
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document.write( "average mph = miles/hours = 800 / (8 1/3) = 96 </SPAN>\n" );
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