SOLUTION: if you drive with a speed of 20km/hr, how fast you must go again returning by the same route for your average speed to be 40km/hr

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Question 409917: if you drive with a speed of 20km/hr, how fast you must go again returning by the same route for your average speed to be 40km/hr
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
if you drive with a speed of 20km/hr, how fast you must go again returning by the same route for your average speed to be 40km/hr
:
I don't think it is possible to go fast enough to average 40 km/hr
:
Let s = speed required to average a round trip speed of 40 km/hr
Let d = one-way distance
:
d%2F20 + d%2Fs = %282d%29%2F40
multiply equation by 40s
2sd + 40d = 2sd
divide thru by d
2s + 40 = 2s
You can see this is not a valid equation, so not possible
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