Question 116562: A Car travels downhill at 72 mph, on the level at 63 mph, and uphill at 56 mph. The trip from point A to point B takes 4 hours, and the return trip takes 4 hours, 40 minutes. What's the distance between points A & B? Please give me the correct formulas/steps to work this problem out.
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! A Car travels downhill at 72 mph, on the level at 63 mph, and uphill at 56 mph. The trip from point A to point B takes 4 hours, and the return trip takes 4 hours, 40 minutes. What's the distance between points A & B?
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Let distance on level ground be "x".
Let distance uphill be "y".
Let distance downhill be "z".
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Time = distance/rate
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Note: uphill in one direction is downhill in the other; and vice versa.
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EQUATIONS:
level time + uphill time + downhill time = total time
x/63 + y/56 + z/72 = 4 hrs
x/63 + y/72 + z/56 = 4 2/3 hrs
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Subtract to get:
y(1/72 - 1/56) + z(1/56 -1/72) = 2/3
y(-16/(72*56)) + z(16/(72*56)) = 2/3
-16y + 16z = (2/3)72*56
-16y + 16z = 48*56
-y+z = 3*56
-y+z = 168
z = 168+y
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Question:
Do you have any more information that might help to resolve
the value of y or of z?
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Cheers,
Stan H.
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