SOLUTION: 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 th

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Question 1176266: 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?
Found 2 solutions by josgarithmetic, ikleyn:
Answer by josgarithmetic(39616)   (Show Source): You can put this solution on YOUR website!
First mason, 12 hours for 1 job
Second mason, 10 hours for 1 job
Time for second mason to finish, for the question, m.

-------------Solve this for m.
Answer by ikleyn(52776)   (Show Source): You can put this solution on YOUR website!
.
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?
~~~~~~~~~~~~ 

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   =  = 5 hours to complete that half 

and the entire job / (the entire wall).    ANSWER

Solved.

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It is  MENTAL  solution by  REASONING.



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