<PRE><B>Question 10257</B>

  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 = {{{120/40}}} = 3 hrs.

  While coming from B to A @ 60mph
  the time taken is = {{{120/60}}} = 2 hrs.

  Total distance travelled = 240 miles 
  Total time taken to cover= 3+2 = 5 hrs.

  So the average speed = {{{240/5}}} = 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

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