SOLUTION: To save fuel on the 240 km trip to their cottage, the smith family reduce their usual average speed by 20 km/h. This meant that their trip took 1 hour more than usual. What is thei

Algebra ->  Customizable Word Problem Solvers  -> Travel -> SOLUTION: To save fuel on the 240 km trip to their cottage, the smith family reduce their usual average speed by 20 km/h. This meant that their trip took 1 hour more than usual. What is thei      Log On

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Question 975668: To save fuel on the 240 km trip to their cottage, the smith family reduce their usual average speed by 20 km/h. This meant that their trip took 1 hour more than usual. What is their average speed?
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
To save fuel on the 240 km trip to their cottage, the smith family reduce their usual average speed by 20 km/h. This meant that their trip took 1 hour more than usual. What is their average speed?
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Faster trip DATA:
distance = 240 km ; rate = r km/hr ; time = d/r = 240/r hrs
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Slower trip DATA:
distance = 240 km ; rate = r-20 km/hr ; time = 240/(r-20) hrs
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Equation:
slower time - faster time = 1 hr
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240/(r-20) - 240/r = 1
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240r - 240r + 240*20 = r(r-20)
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r^2 - 20r - 20*240 = 0
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Ans: r = 80 km/hr
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Cheers,
Stan H.
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