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 #628482 by MathTherapy(10552)\"\" \"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. Find it's average speed for the last 20% of the trip.
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Let distance traveled on entire journey be D
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document.write( "Then distance traveled on 1st 80% = .8D
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document.write( "Time taken to travel 1st 80% of journey = \".8D%2F120\"
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document.write( "Let speed during last 20% of trip be S
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document.write( "Since distance traveled on last 20% = .2D, then
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document.write( "Time taken to travel last 20% of journey = \".2D%2FS\"\r
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document.write( "Total distance: D 
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document.write( "Total time: \".8D%2F120+%2B+.2D%2FS\"
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document.write( "Average speed = Total distance, divided by total time, OR
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document.write( "\"90+=+D%2F%28.8D%2F120+%2B+.2D%2FS%29\"
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document.write( "\"90%28.8D%2F120+%2B+.2D%2FS%29+=+D\" ----- Cross-multiplying
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document.write( "\"90+%2A+%28.8D%2F120%29+%2B+90%28.2D%2FS%29+=+D\"
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document.write( "\".6D+%2B+18D%2FS+=+D\"
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document.write( ".6DS + 18D = DS ------- Multiplying by LCD, S
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document.write( "D(.6S + 18) = D(S) ---- Factoring out GCF, D
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document.write( ".6S + 18 = S
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document.write( "18 = S - .6S
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document.write( "18 = .4S
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document.write( "S, or speed on 2nd leg of journey = \"18%2F.4\", or \"highlight_green%2845%29\" km/h \n" );
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