SOLUTION: A reconnaissance plane flies 600 km away from its base at 180 km/h, then flies back to its base at 420 km/h. What is its average speed?

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Question 393977: A reconnaissance plane flies 600 km away from its base at 180 km/h, then flies back to its base at 420 km/h. What is its average speed?
Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!
Use the harmonic means of the two rates:
2%2F%281%2F180+%2B+1%2F420%29+=+252 km/h, the average speed of the plane.