Students make the trip to Los Angeles at an average speed of 40mph and the trip back at an average speed of 60 mph. Find their average speed for the entire trip. (It's Not 50 mph)

Please help me answer this question and if possible, can u show the steps of solving it. Thank You soo much.

colbtech

I think that I am missing something here!
If the answer is not 50, then there must be other factors to give a different answer.

From your question, the distance and time is irrelevant. It is a simple matter of adding the two average speeds and dividing by 2, which gives an answer of 50. ?????

Dr D

Just enter any random distance for the trip; say 200 miles. One way at 40 mph avg = 5 hours. On the return trip at 60 mph avg = 3.333 hours. Total round trip of 400 miles took 8.333 hours. 400/8.333 = 48mph avg.

kp2171

dr d is correct.

the assumption that is wrong with adding 40 + 60 / 2 is that you are driving a fixed distance (point A to LA and then back), not a fixed time (one hour there and the same time back). does it make sense that you are going to be driving longer at 40 mph than on the way home?

so since the average speed is the overall distance divided by time, you need to figure out how long you would be in the car both ways. dr d's example works.

just to give another ex, if your distance was 500 miles to LA, youd drive 40 mph, which gives 500miles * (1/40 mph) = 12.5 hours to go 500 miles.

then if you drive the same 500 miles back at 60mph youd get 500 miles * (1/60mph) = 8.33 hours to go 500 miles.

so 1000 miles / (12.5+8.3 hours) = 1000/20.8 = 48.1 miles per hour.

im guessing this is for a physics class you are taking. the hardest part of this problem is realizing you needed to simply start with a theoretical distance and use the speed to come up with time.

BigD

Thank You every body for helping. I just realizes how easy it is if u think it through more carefully. Thanx again

colbtech

Yes, thanks folks! Makes sense your way.