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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