Question 1130918
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There is a way to get the solution mentally in two easy steps.



<pre>
Step 1.  It is clear, that the basic equation is

             W*(8W + 10) = 7500.


         Multiply both sides by 8:

             8W*(8W+10) = 8*7500,    or   8W*(2W+10) = 60000.




Step 2.  What are two numbers that differ by 10 and give 60000 when multiplied ?

             Look into  {{{sqrt(60000)}}} = 244.95.


         Then in 5 seconds you get  that the numbers are  240 and 250.

         After that, you final move is 

              8W = 240,   which  implies  W = 240/8 = 30.
</pre>

Solved.