SOLUTION: A motorist travels A to B at a speed at 40 km/h and returns at speed of 60 km/h. his average speed will be:

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Question 890470: A motorist travels A to B at a speed at 40 km/h and returns at speed of 60 km/h. his average speed will be:
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
A motorist travels A to B at a speed at 40 km/h and returns at speed of 60 km/h. his average speed will be between 40 & 60.
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Use d = r*t
t = d/r
d = distance one way.
Total time = d/40 + d/60
Round trip avg = 2d%2Ft+=+2d%2F%28d%2F40+%2B+d%2F60%29
= 2%2F%281%2F40+%2B+1%2F60%29
= 2*40*60/(40+60)
= 48 km/hr
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Notice it's similar to parallel resistors and parallel flows.
Avg = 2*r1*r2/(r1 + r2)
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Also notice the distance is not a factor.