Very vague question about speed, distance, time

Nov 2014
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It goes like this:

"Ed goes 20mph in one direction, and 50 mph on the return trip. His average speed is?"

I am just not getting the explanation in the book, if anybody could explain how this is done, I would be extremely grateful, thanks
 

skeeter

MHF Helper
Jun 2008
16,217
6,765
North Texas
average speed = (total distance traveled)/(total time required to cover the total distance)

let d = distance in one direction $\implies$ total distance = 2d

time traveling at 20 mph = d/20

time traveling at 50 mph = d/50

total time = d/20 + d/50 = 7d/100

avg speed = (2d)/(7d/100) = (200d)/(7d) = 200/7 mph $\approx$ 28.6 mph
 
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Reactions: 1 person
Feb 2015
2,255
510
Ottawa Ontario
...or make up li'l scenario:

@20............100.............>5
2<[email protected]

200 miles travelled in 7 hours, right?