SOLUTION: John drives from Town A to Town B , a distance of 720 km , at a constant speed. When he returns from Town B to A, he saves an hour of travel time by increasing his average speed
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Question 335060: John drives from Town A to Town B , a distance of 720 km , at a constant speed. When he returns from Town B to A, he saves an hour of travel time by increasing his average speed by 10 km/h. find the total time taken for the whole journey(to and fro)
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
John drives from Town A to Town B , a distance of 720 km , at a constant speed.
distance = 720 km ; rate = x km/h ; time = 720/x hrs.
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When he returns from Town B to A, he saves an hour of travel time by increasing his average speed by 10 km/h.
distance = 720 km ; rate = (x+10) km/h ; time = 720/(
Find the total time taken for the whole journey(to and fro)
Equation:
time to - time from = 1 hr
720/x - 720/(x+10) = 1
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Multiply thru by x(x+10) to get:
720(x+10) - 720x = x(x+10)
7200 = x^2+10x
x^2+10x-7200 = 0
(x+90)(x-80) = 0
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x = 80 km/h ; time to = 720/80 = 9 hrs.
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x+10 = 90 km/h ; time from = 720/90 = 8 hrs.
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Total time = 9+8 = 17 hrs.
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Cheers,
Stan H.
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