SOLUTION: My math problem is this: A car goes from point A to point B, at a rate of 40 mph. Then the same car turns around and goes from point B to point A, at a rate of 60 mph. What is the

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Question 10257: My math problem is this:
A car goes from point A to point B, at a rate of 40 mph. Then the same car turns around and goes from point B to point A, at a rate of 60 mph. What is the average speen of this car? My teacher said that it was not 50 mph. I am very confused on this and would like a thurough explination. Thank you so much for this. :D I need all the help, and it is very much appreciated. I've spent time trying to figure out the answer to this, and I've come up with an average speed of 55 mph, but I am not sure how I got that, and I don't know how to check if it is right. Please help me and thank you.
Answer by gsmani_iyer(201) About Me  (Show Source):
You can put this solution on YOUR website!

Let us say the distance between A and B = 120 miles. (Why 120?)
So while going from A to B @ 40mph,
the time taken is = 120%2F40 = 3 hrs.
While coming from B to A @ 60mph
the time taken is = 120%2F60 = 2 hrs.
Total distance travelled = 240 miles
Total time taken to cover= 3+2 = 5 hrs.
So the average speed = 240%2F5 = 48 mph. Answer
why I have taken 120 is because 120 is the LCM of both 40 and 60 and
120 is divisible by both 40 and 60. It is the only reason. Then it will
be easy to solve the problem.
I hope you understood this.
gsm