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Thread: Percentages help

  1. #1
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    Question Percentages help

    Can someone please explain how they arrive at the answer? Thanks in advance.


    If notreatment has been given within 3 hours after injury to a certain organ, theorganís function starts decreasing by 20% each hour. If no treatment has beengiven with 6 hours after injury, approximately how much function will remain?

    Answer
    At theend of three hours, the organ still has 100% function.
    After 4hours, it has 80% of that 100%, or (0.8)(1), or 0.8.
    After 5hours, it has 80% of the 80% it had at the end of four hours: (0.8)(.8) equals64%.
    After 6hours, it has 80% of the 64% it still had after five hours: (0.8)(0.64) equals 0.512.

    Can youplease explain why 80% is constant after 4 hours not decreasing anadditional 20%?








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  2. #2
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    Re: Percentages help

    Reducing an amount by 20% is the same as taking 80% of that amount.

    If you take 60% (which is what you might be thinking), then that is reducing the amount by 40%.

    The amount at the end of an hour is 80% of the amount at the beginning of that hour.
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  3. #3
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    Re: Percentages help

    Thanks so much. Lightbulb moment.
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  4. #4
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    Re: Percentages help

    ...or use future value of 1 dollar at -20% (crooked Bank!) over 3 periods:
    1(1 - .20)^3 = .512
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