Question 726221: rachel drove 780 miles. if she had drove 5 mph faster, the trip would have taken 1 hour less. How fast did she drive? Answer by stanbon(75887) (Show Source):
You can put this solution on YOUR website! rachel drove 780 miles. if she had drove 5 mph faster, the trip would have taken 1 hour less. How fast did she drive?
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Slower trip DATA:
distance = 780 ; rate = r mph ; time = 780/r hours
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Faster trip DATA:
distance = 780 ; rate = r+5 mph ; time = 780/(r+5) hours
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Equation:
time - time = 1 hour
780/r - 780/(r+5) = 1 hr
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780r + 780*5 - 780r = r(r+5)
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r^2+5r-5*780 = 0
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r = 60 mph
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Cheers,
Stan H.
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