Question 1197567
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The solution by @josgarithmetic is conceptually  TOTALLY  wrong.


It is wrong,  since this airplane averages  150 mph in  STILL  AIR 
(the part of the condition,  which is  {{{highlight(highlight(MISSED))}}}  in the post).


Again :   150 mph is the average speed of the plane in  STILL  AIR, 
but  NOT  IN  THIS  round trip:  150 mph relates to  TOTALLY  DIFFERENT  conception.



        The post itself has a  HUGE  DEFICIENCY:  it missed 

        to determine correctly all the participating values/conditions.



Taking it into the consideration, the problem, as it is worded in the post,

is ambiguous, which is not allowed for Math problems.



Therefore,  my advise to the visitor is to throw this  " problem "  to the closest garbage bin

and to  {{{highlight(highlight(MEMORIZE))}}}  that only mathematically correct problems are the subject of consideration at this forum.



            Each correct mathematical problem is a piece of art.

        What is not piece of art - is not a correct mathematical problem.



Exactly as the wife of an emperor should be beyond suspicions,

every  Math problem must be ideally and absolutely correct - always.