document.write( "Question 759862: A motorist travels 120 miles from Antwerp to Brussels at an average of 40 mph. She returns over the same road at X mph. Her average rate for the whole trip is 48 mph. What is the value of X?\r
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Algebra.Com's Answer #462269 by Alan3354(69443)\"\" \"About 
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A motorist travels 120 miles from Antwerp to Brussels at an average of 40 mph. She returns over the same road at X mph. Her average rate for the whole trip is 48 mph. What is the value of X?
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\n" ); document.write( "120 miles at 40 mi/hr takes 3 hours.
\n" ); document.write( "The round trip is 240 miles, at 48 mi/hr avg --> 5 hours total.
\n" ); document.write( "--> 2 hours for the return
\n" ); document.write( "120 mi/2 hr = 60 mi/hr
\n" ); document.write( "x = 60 mi/hr
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\n" ); document.write( "Notice that a round-trip at 40 & 60 is not the average of 40 & 60.
\n" ); document.write( "The average is always less than the average of 2 unequal speeds.
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\n" ); document.write( "Avg for RT = 2*r1*r2/(r1 + r2)
\n" ); document.write( "For 60 & 40,
\n" ); document.write( "Avg - 2*60*40/(60+40) = 48 mi/hr
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