document.write( "Question 1156291: During the first 30 miles of city driving, you average 40 miles per hour. For the remainder of the trip, you drive on a highway at a constant rate of 85 miles per hour. Your average speed for the entire trip is given by
\n" ); document.write( "r(x) = (30 + x)/3/4+1/85x\r
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\n" ); document.write( "\n" ); document.write( "where x is the number of miles you have driven on the highway.
\n" ); document.write( "(a) How far will you need to drive on the highway to bring your average speed up to 60 miles per hour? \n" ); document.write( "

Algebra.Com's Answer #779014 by josgarithmetic(39618) $\"\"$ $\"About$

You can put this solution on YOUR website!
You want to show your function as r(x) = (30 + x)/(3/4+x/85).\r
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document.write( "PART      SPEED       TIME        DISTANCE\r\n" );
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document.write( "first       40         30/40        30\r\n" );
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document.write( "last       85          x/85         x\r\n" );
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document.write( "TOTALS              x/85+3/4      x+30\r\n" );
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\n" ); document.write( "function for average rate r for whole trip:\r
\n" ); document.write( "\n" ); document.write( " $\"r%28x%29=%28x%2B30%29%2F%28x%2F85%2B3%2F4%29\"$ \r
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\n" ); document.write( "\n" ); document.write( "With algebra steps, rewritten as $\"r%28x%29=%28340x%2B10200%29%2F%284x%2B255%29\"$ \r
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\n" ); document.write( "\n" ); document.write( "To answer the question \"a\", let r(x) equal 60, and solve the equation for x.
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