SOLUTION: One man and 2 boys can do a piece of work in 12 days, which can also be done by 3 men and 1 boy in 6 days. Howlong it would take for one alone man to complete the work.

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Question 71338: One man and 2 boys can do a piece of work in 12 days, which can also be done by 3 men and 1 boy in 6 days. Howlong it would take for one alone man to complete the work.
Answer by 303795(602) About Me  (Show Source):
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If one man and two boys take twelve days then two men and four boys would take only six days. (twice as many people take half the time.)
But you are also told three men and one boy take six days
3M + 1B = 2M + 4B
ie 1M = 3B so one man does the same work as three boys.
Therefore five boys (equivalent to one man and two boys) would take twelve days to do the job. One boy would take five times as long so it would take one boy sixty days to do the job.
Three boys would take one third as long so they would take 20 days and one man is equivalent to three boys so one man will take 20 days.