document.write( "Question 1140236: You travel the first 48 miles of a journey at an average of 36 mph and the second 48 miles at an average of v mph. What must be v if you want to average 45 mph over the 96 mile journey?
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Algebra.Com's Answer #760725 by Alan3354(69443) $\"\"$ $\"About$

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You travel the first 48 miles of a journey at an average of 36 mph and the second 48 miles at an average of v mph. What must be v if you want to average 45 mph over the 96 mile journey?
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\n" ); document.write( "Avg speed of a round trip or of equal parts is:
\n" ); document.write( "Avg = 2*r1*r2/(r1 + r2)
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\n" ); document.write( "45 = 2*36*r2/(36+r2)
\n" ); document.write( "45*(36+r2) = 72r2
\n" ); document.write( "1620 + 45r2 = 72r2
\n" ); document.write( "27r2 = 1620
\n" ); document.write( "r2 = 60 mi/hr
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\n" ); document.write( "IMO, this is a formula you should remember. It's similar to parallel work, parallel flow, parallel resistors, etc. Only the factor of 2 is different.
\n" ); document.write( "You can remember it, or not.
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\n" ); document.write( "It's also the basis for the famous Michelson-Morley experiment that showed no effects of the \"ether\" and dispelled belief in the existence of the ether. Ether is now stored in the same closet as phlogiston.
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