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Math Help - Percentages

  1. #1
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    Question Percentages

    I haven't done much math since high school, so please be patient with me.

    100 * 0.8 = 80

    80 * X = 100

    X is equal to 1.25, which was pretty easy to find after trial and error, but the trial and error process takes a lot longer with something like this:

    5,680 * 0.802 = 4555.36

    4555.36 * X = 5,680

    X is equal to ~1.2468827930174563591022444, but that took forever to find through trial and error. How can I easily find X?
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  2. #2
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    pickslides's Avatar
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    Re: Percentages

    80x = 100 therefore x = 100/80
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  3. #3
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    e^(i*pi)'s Avatar
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    Re: Percentages

    You can take the reciprocal of the number you're replacing. For your example above note that X = \dfrac{1}{0.8}

    edit: This is exactly the same as Pickslides' answer. You can multiply my answer by 100/100 to get his

    For your second example it will be X = \dfrac{1}{0.802}. Normally we'd just use a calculator to solve for X but you can do it using fractions.

    \dfrac{1}{0.802} \times \dfrac{1000}{1000} = \dfrac{1000}{802}. This will cancel by at least 2.
    Last edited by e^(i*pi); July 6th 2011 at 04:37 PM. Reason: see post
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  4. #4
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    Re: Percentages

    Thanks guys!
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