Question 1154666
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            I'd like to contribute my  2  cents to this problem's solution.



<pre>
It is clear that we can exclude the first 2/3 of the journey from the consideration,
since at this part there is no delay comparing with the standard schedule.


The difference arises on the remained 1/3 distance, which is 60 miles.


For this part of 60 miles, we have a regular time  {{{60/x}}}, where x is the regular speed.


With the speed of {{{(3/4)x}}}, the spent time is  {{{60/((3/4)x)}}} = {{{80/x}}}.


So, the delay equation is


    {{{80/x}}} - {{{60/x}}} = {{{1/2}}}   (which is half of an hour)


From the equation,  


    {{{20/x}}} = {{{1/2}}};

hence,

    x = {{{20/((1/2))}}} = 2*20 = 40 kilometers per hour.    <U>ANSWER</U>
</pre>

Solved.


I hope that my setup is simpler and, therefore, more attractive.