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. (NO, the answer is not 400

Question 252822: 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. (NO, the answer is not 400 mph.)
Found 2 solutions by Alan3354, richwmiller:
Answer by Alan3354(69443) (Show Source): You can put this solution on YOUR website!
Here's a similar problem I did yesterday.
If you need further help, or to check your work, email via the thank you note.
==================================================================
A cyclist bikes x distance at 10 miles per hour and returns over the same path at 8 miles per hour. What is the cyclist's average rate for the round trip in miles per hour?
---------------------
d= rt --> t = d/r
t = x/10 + x/8 = 9x/40
r = 2d/t = 2x/t --- 2x for the round trip
r = (2x/1)/(9x/40) = 80x/9x
r = 80/9 = 8.888... mph
---------------------------
It's not the average, 9 mph, because he spent more time going 8 mph than he did going 10 mph.
---------------
That's the basis of the famous Michelson-Morley experiment that disproved the existence of the "ether" is space.
Answer by richwmiller(17219) (Show Source): You can put this solution on YOUR website!
No, it isn't 400 but the difference is not worth the bother. I doubt the speedometers are that accurate anyways, especially if they are analog.
r=distance/time
time=d/380+d/420
distance=2d
r=2d/(d/380+d/420)
r=399
RELATED QUESTIONS
Flying east between two cities, a planes speed is 380 mph. On the return trip, it flies... (answered by Alan3354)
Flying east between two cities, a plane's speed is 380 MPH. On the return trip, it flies... (answered by Alan3354)
A jet flies from New York to Atlanta at an average rate of 420 mph. On the return trip,... (answered by jim_thompson5910)
plane flies 420 mph in still air. With wind, a trip from a to b takes 10 minutes less... (answered by ankor@dixie-net.com)
I need some assistance please. Two cities are 1000 miles apart. On the first flight a... (answered by ewatrrr)
A plane driver was needed at the production site of a SYFY movie. The average speed of... (answered by ewatrrr,josgarithmetic)
A jet flies between two major cities at a rate of 400 miles per hour. On the return trip, (answered by Alan3354)
A plane flies from Worcester to Chicago at an average rate of 380 mph and returns along... (answered by richwmiller)
A plane flies 6 hours against the wind. The return trip takes 5 hours. The plane's... (answered by richwmiller)