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Math Help - Inverse

  1. #1
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    Unhappy Inverse

    If it takes 9 people to collect 10 kg of wood in 12 hours. How long does it take 7 people to collect 7.5 kg of same wood?

    Last edited by joshuaa; March 12th 2012 at 12:47 PM.
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  2. #2
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    Re: Inverse

    Quote Originally Posted by joshuaa View Post
    If it takes 9 people to collect 10 kg of wood in 12 hours. How long does it take 7 people to collect 7.5 kg of same wood?

    one person collects (10/9) kg wood in 12 hrs ...
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  3. #3
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    Re: Inverse

    so in the second side one person collects 7.5/7 in unknown hours. I still need to know the time???
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  4. #4
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    Re: Inverse

    (number of people)(wood collection rate for 1 person)(time) = total wood collected
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    Re: Inverse

    If we plug the values of the left side
    (9)(10/9)(12) = 10
    120 = 10 is the final answer which is not correct

    If we plug the values of the right side
    (7)(7.5/7)(X) = 7.5
    X = 1 is the final answer which I think is not correct too

    Explain More...
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  6. #6
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    Re: Inverse

    Quote Originally Posted by skeeter View Post
    (number of people)(wood collection rate for 1 person)(time) = total wood collected
    one more time ...

    (9 \, people) \cdot \left(\frac{(10/9) \, kg}{12 \, hrs}\right) \cdot (12 \, hrs) = 10 \, kg

    now do it for 7 people and and 7.5 kg and solve for t
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  7. #7
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    Re: Inverse

    (7)[(7.5/7)kg/t](t) = 7.5
    i end up with 7.5=7.5 because t and t was cancelled
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    Re: Inverse

    (7 \, people) \cdot \left(\frac{(10/9) \, kg/person}{12 \, hrs}\right) \cdot (t \, hrs) = 7.5 \, kg

    solve for t
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  9. #9
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    Re: Inverse

    Thanks a lot. It was so helpful
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  10. #10
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    Re: Inverse

    Why the rate was not [(7.5/7)/X]?
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