SOLUTION: a man drives for 90 miles in the city, when he gets to the highway he increased his speed by 20 mph and drove for 130 miles. if he drove for 4 hours how fast did he drive in the ci

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Question 1008472: a man drives for 90 miles in the city, when he gets to the highway he increased his speed by 20 mph and drove for 130 miles. if he drove for 4 hours how fast did he drive in the city
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
a man drives for 90 miles in the city, when he gets to the highway he increased his speed by 20 mph and drove for 130 miles. if he drove for 4 hours how fast did he drive in the city
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City DATA:
distance = 90 miles ; rate = r mph ; time = d/r = 90/r hrs
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Hiway DATA:
distance = 130 miles ; rate = (r+20) mph ; time = 130/(r+20) hrs
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Equation::
90/r + 130/(r+20) = 4 hrs
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90(r+20) + 130r = 4r(r+20)
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220r + 1800 = 4r^2 + 80r
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4r^2 -140r - 1800 = 0
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r^2 - 35r - 450 = 0
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Ans: r = 45 mph (City speed)
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Cheers,
Stan H.
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