Math Destroyer- Distance problems

[AK28]

Can anyone explain distance problems to me? I can't seem to understand them! Here is an example from Math Destroyer:

Sam travels the 40 miles from Albany to Brickville at 60 mph. At what speed must he travel back from Brockville to Albany so that the average velocity for the round trip is 75 mph?

---

Members don't see this ad.

 

[rdub]

Use the equation for average velocity.... Average Velocity = (Total Distance Travelled)/(Total time passed).

You know the total distance is 80 miles (40 miles there, 40 miles back)
You can calculate the time it took to go from Albany to Brickville (T1) using dimensional analysis (1hr/60miles * 40 miles). The rest should just be plug and chug.

 

[alexis2010]

Since the average speed for the round trip is 75 and the speed and the speed from Albany to brickville is 60, the return seen should be a lot more than 75. That leaves you with either 80 or 100. Now just back solve and use : average speed= total distance/ total time.
100 mph works.

 

[AK28]

Thank you!!

 

[DMikes]

I don't mean to be picky, but does the actual question ask for the average velocity? Average velocity is a measure of displacement/time not distance traveled/time. Thus, the average velocity would be 0, no matter the speed, if the subject returned to their original position.