document.write( "Question 259134: Your average speed on the first half of a car trip is 70.0 km/h. How fast do you have to drive on the second half of the trip to achieve an average speed of 85.0 km/h for the whole trip? \n" ); document.write( "
Algebra.Com's Answer #190792 by stanbon(75887)\"\" \"About 
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Your average speed on the first half of a car trip is 70.0 km/h. How fast do you have to drive on the second half of the trip to achieve an average speed of 85.0 km/h for the whole trip?
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\n" ); document.write( "1st Half DATA:
\n" ); document.write( "distance = x km ; rate = 70 km/h ; time = d/r = x/70 hrs.
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\n" ); document.write( "2nd Half DATA:
\n" ); document.write( "distance = x km ; rate = r km/h ; time = x/r hrs.
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\n" ); document.write( "Total Trip DATA:
\n" ); document.write( "distance = 2x km; rate = 85 km/h ; time = (2x)/85 hrs
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\n" ); document.write( "Equation:
\n" ); document.write( "time + time = total time
\n" ); document.write( "x/70 + x/r = (2x)/85
\n" ); document.write( "1/70 + 1/r = 2/85
\n" ); document.write( "(r+70)/70r = 2/85
\n" ); document.write( "Cross-Multiply:
\n" ); document.write( "140r = 85r + 85*70
\n" ); document.write( "55r = 85*70
\n" ); document.write( "r = 108.18 kph (rate needed in the 2nd half of the trip)
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\n" ); document.write( "Cheers,
\n" ); document.write( "Stan H. \n" ); document.write( "
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