the job is 12*6 = 72 man-hours of work.
In 1 hour, the 12 men have done 1/6 of the work, leaving 60 man-hours to do.
That will take 20 men 3 hours to finish up.
twelve men take 6 hours to finish a piece of work. after the 12 men have worked for 1 hour, the contractor decides to call in 8 more men so that the work can be completed earlier. how many more hours would 20 men take to compete the remaining work?
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