QR from Ada pRactice

[promolion]

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A person travels to work at an average
speed of 40 mph, and returns home at 60
mph. Which of the following, in mph, is the
average speed for the entire trip?
A. 45
B. 46
C. 48
D. 52
E. 54

No clue how to find it without the time.....any help will be appreciated. thx.

 

[drgreen]

Assume the work is 1 mile away, for simplicity.

average speed=total distance/total time

total distance: 2 miles

total time:
on the way there it takes him 1/40 hrs, on the way back it takes him 1/60 hrs
so total time=1/40+1/60=1/24hrs

average speed=2/(1/24)=48

 

[Streetwolf]

Yeah so I would assume work is 120 miles away for even more simplicity haha.

That way it's 3 hours to get there and 2 hours to get home.

 

[drgreen]

Yeah so I would assume work is 120 miles away for even more simplicity haha.

That way it's 3 hours to get there and 2 hours to get home.

3+2=5

240/5=48

two simple calculations, beautifull