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Math Help - Inverse proportion/Direct proportion question

  1. #1
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    Inverse proportion/Direct proportion question

    Question: If 3 workers are required to build a 10m drain in 5 days, how many days will it take for 5 workers to build a 30m drain?

    My first step is to calculate the inverse proportion of workers and days then I am stuck with the length of the drain. How do I go around to solve it?
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  2. #2
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    Re: Inverse proportion/Direct proportion question

    Quote Originally Posted by FailInMaths View Post
    Question: If 3 workers are required to build a 10m drain in 5 days, how many days will it take for 5 workers to build a 30m drain?

    My first step is to calculate the inverse proportion of workers and days then I am stuck with the length of the drain. How do I go around to solve it?
    3 "identical" workers take 5 days to build 10 metres.
    1 worker, working alone takes 3 times as long, that's 15 days for 10 metres,
    which is 45 days for 30 metres.

    5 workers take a fifth of the time.
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  3. #3
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    Re: Inverse proportion/Direct proportion question

    Quote Originally Posted by Archie Meade View Post
    3 "identical" workers take 5 days to build 10 metres.
    1 worker, working alone takes 3 times as long, that's 15 days for 10 metres,
    which is 45 days for 30 metres.

    5 workers take a fifth of the time.
    Oh, I get it now, I thought it required complex stuff for the solution, stupid me

    Thanks =)
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  4. #4
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    Re: Inverse proportion/Direct proportion question

    You could formulate the problem also, using the concept of "man days".

    It takes 5(3) "man days" to build 10 metres

    so it takes 5(3)(3) = 5(9) "man days" to build 3(10) = 30 metres.

    That shows straight off how many days are required for 5 men.
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