SOLUTION: Flying east between two cities, a plane's speed is 380 MPH. On the return trip, it flies at 420 MPH. Find the average speed over the whole round trip. -My teacher wrote on the pape

Question 377770: Flying east between two cities, a plane's speed is 380 MPH. On the return trip, it flies at 420 MPH. Find the average speed over the whole round trip. -My teacher wrote on the paper that the answer is not 400 MPH. Thank you very much!
Answer by Alan3354(69443) (Show Source): You can put this solution on YOUR website!
I did this one 2 days ago, you can look up the detailed solution on the site.
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avg speed for the round trip = 2*r1*r2/(rq + r2)
= 2*380*420/(800)
= 399 mph

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