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Question 460758: A man and a boy can do in 15 days of work in which would be done by 7 men and 9 boys in 2 days. How long would it take one man to do it alone?
Answer by ankor@dixie-net.com(22740)   (Show Source):
You can put this solution on YOUR website! A man and a boy can do in 15 days of work in which would be done by 7 men and 9 boys in 2 days.
How long would it take one man to do it alone?
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Let md = 1 man-day
Let bd = 1 boy-day
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Let the completed job = 1
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"A man and a boy can do in 15 days of work"
15md + 15 bd = 1
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"which would be done by 7 men and 9 boys in 2 days."
14 md + 18 bd = 1
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Multiply the 1st equation by 6, multiply the 2nd equations by 5
90md + 90 bd = 6
70md + 90 bd = 5
------------------subtraction eliminates bd, find md
20 md = 1
20 man-days are required to do the job, therefore it would take 1 man 20 days to do the job
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