document.write( "Question 142042: You are making a trip of 300 miles. After one third of the way, you determine that you have averaged 45 miles per hour. How fast should you average over the remaining trip in order to average 70 miles per hour for the entire trip? \n" ); document.write( "
Algebra.Com's Answer #103447 by checkley77(12844)\"\" \"About 
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300/x=70
\n" ); document.write( "70x=300
\n" ); document.write( "x=300/70
\n" ); document.write( "x=4.2857 hours is the total trip time.
\n" ); document.write( "100/45+200/x=4.2857
\n" ); document.write( "2.22+200/x=4.2857
\n" ); document.write( "200/x=4.2857-2.22
\n" ); document.write( "200/x=2.06
\n" ); document.write( "2.06x=200
\n" ); document.write( "x=200/2.06
\n" ); document.write( "x=97.09 mph is the required speed for the last 200 miles to average 70 mph for the entire 300 mile trip.
\n" ); document.write( "proof:
\n" ); document.write( "100/45+200/97.09=300/70
\n" ); document.write( "2.22+2.06=4.2857
\n" ); document.write( "4.28~4.2857\r
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