document.write( "Question 1012510: A train averaged 120km/h for the first 80% of a trip and 90km/h for the whole trip. Find it's average speed for the last 20% of the trip. \n" ); document.write( "

Algebra.Com's Answer #628466 by ikleyn(52794) $\"\"$ $\"About$

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\n" ); document.write( "A train averaged 120km/h for the first 80% of a trip and 90km/h for the whole trip.
\n" ); document.write( "Find it's average speed for the last 20% of the trip.
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document.write( "Let D be the entire distance.\r\n" );
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document.write( "The train covered first 80% of the entire distance, i.e. 0.8*D, at the average speed of 120 . \r\n" );
document.write( "Hence, it spent  hours to cover this part. \r\n" );
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document.write( "Let u be the speed of the train on the second (20%) part of the trip.\r\n" );
document.write( "Then the train spent  hours to cover the second part. \r\n" );
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document.write( "Thus the full time for the trip was\r\n" );
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document.write( "t =  +     (1)\r\n" );
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document.write( "hours. We are given that the average speed was 90 . \r\n" );
document.write( "It means that the whole distance divided by the full time is 90 . \r\n" );
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document.write( "It gives you an equation\r\n" );
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document.write( " = 90.\r\n" );
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document.write( "Cancel the factor D in the numerator and the denominator. You will get\r\n" );
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document.write( " = 90.\r\n" );
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document.write( "It is your equation to find the speed u.\r\n" );
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document.write( "Let us simplify it step by step:\r\n" );
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document.write( " = 90  ----->   = 3  ----->  4u = 3*(0.8*u + 24)  ----->  4u = 2.4u + 72  ----->  4u - 2.4 u = 72  ----->  1.6u = 72,\r\n" );
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document.write( "u =  = 45 . \r\n" );
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document.write( "It is the speed of the train on the second part of the trip.\r\n" );
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document.write( "The solution is completed.\r\n" );
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document.write( "Answer. The speed of the train on the second part of the trip was 45 .\r\n" );
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