Question 1176266
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A cement mason can construct a retaining wall in 12 h. 
A second mason requires 10 h to do the same job. 
After working alone for 6 h, the first mason quits. 
How long will it take the second mason to complete the wall?
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<pre>
After working 6 hours, the first mason, completed one half of the job;  
another half remained to be completed by the second mason.


So, the second mason needs  {{{((1/2))/((1/10)))}}} = {{{10/2}}} = 5 hours to complete that half 

and the entire job / (the entire wall).    <U>ANSWER</U>
</pre>

Solved.


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It is &nbsp;MENTAL &nbsp;solution by &nbsp;REASONING.