SOLUTION: 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. How many more hours would 20 men take t

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Question 888134: 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. How many more hours would 20 men take to complete the remaining work
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Twelve men take 6 hours to finish a piece of work.
In 1 hour, the 12 men will finish 1/6 of the work
( 1 job ) / ( 6 hrs ) = ( 1/6 of a job ) / ( 1 hr )
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That means there is +1+-+1%2F6+=+5%2F6+ of the job
left to do.
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If 12 men take 6 hours to finish a piece of work,
1 man will take 12 times as long, to finish the work, so
( 1 job ) / ( 6*12 = 72 hrs ) = rate of working for 1 man, or
+1%2F72+
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After 1 hour, there are a total of +12+%2B+8+=+20+ men working
20 men will work 20 times as fast as 1 man on the +5%2F6+
of a job that remains, so
Let +t+ = hours for the 20 men to finish the job
+20%2A%28+1%2F72+%29+=+%28%28+5%2F6+%29%29+%2F+t+
+20%2F72+=+5%2F%286t%29+
+5%2F18+=+5%2F%28+6t%29+
Multiply both sides by +18t+
+5t+=+15+
+3+
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It will takes the 20 men 3 more hours to
complete the remaining work
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Hope I got it