Question 1208315
.
Two trains are approaching each other on parallel tracks.  Train A is 1/5 of a mile in length. 
It travels east at a speed of 40 mph.  Train B is 1/8 of a mile in length. It travels west at a speed of 50 mph.


From the moment the trains meet(that is when their noses touch the same plane perpendicular to the tracks), 
how much time elapses until their tails completely pass one another.
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        For your better understanding,  here I will show you 

        how to solve the problem without using equation.



<pre>
The starting moment for our consideration is when the trains noses 
touch the same plane perpendicular to the tracks.


At this time moment, the ending points of the trains are at the distance
equal to the sum of the lengths of trains, i.e.  

    {{{1/5+1/8}}} = {{{5/40 + 5/40}}} = {{{13/40}}}  of a mile.


These two ending points moves/approach toward each other with the speed, 
which is the sum of the speeds of the trains, i.e. 40 + 50 = 90 miles per hour. 
It is the relative speed approaching the ending points.


The process will complete when the ending points will meet each other.


The time is  

     {{{the_initial_distance_between_end_points/the_relative_speed_of_approaching}}}= {{{((13/40))/90}}} = {{{13/3600}}} of an hour,

which is 13 seconds.
</pre>

Solved.


It is how physicists think when they solve such problems.