Question 1136891
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One half of the race is 20/2 = 10 kilometers, same as the second half.


The time spent on the first half is  {{{10/x}}}  hours.


The time spent on the second half is  {{{10/(x-2)}}}  hours  (since the speed there is (x-2) km/h).


Hence, the total time expression is


    Total time = {{{10/x}}} + {{{10/(x-2)}}}    hours.
</pre>

Having this basic expression, you can transform it in any (equivalent) way, on your choice.


Solved.