document.write( "Question 1137736: On a journey of 200 km, a motorist found that if he were to increase his average speed by 2 km/h, the journey would take 15 minutes less. Calculate his average speed \n" ); document.write( "

Algebra.Com's Answer #755609 by math_helper(2461) $\"\"$ $\"About$

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document.write( "d=rt
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document.write( "Using units of hours for time, km for distance:\r
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document.write( "r=d/t = 200/t     (1)\r
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document.write( "We are given:
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document.write( "r+2 = d/(t-1/4)  (2)     \r
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document.write( "Solving each for t and then setting them equal to eliminate t:
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document.write( "Re-arranging and then simplifying:
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document.write( "Solving:
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document.write( "Taking positive result:     km/hr\r
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document.write( "Check:  Add 2km/hr to the above:  41.012 km/hr\r
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document.write( "At 39.012km/hr the trip takes  200km/(39.012km/hr) = 5.1266hr
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document.write( "At 41.012km/hr the trip would take 200km/(41.012km/hr) = 4.8766hr\r
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document.write( "The difference is  0.25hr which is 15 minutes.
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