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Math Help - Finding Original Amount

  1. #1
    Newbie
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    Finding Original Amount

    If I have $20 at 7% tax, I get a total of $21.40. If I use this equation:

    $21.40/1.07 = $20, it will give me by base amount before the tax was added on.

    What I need to know is if I have ($10 + ($10 + (10 * 7%))), I get a total of $20.70. How do I find out what the base amount of this is? I cant use $20.70/1.07 to get my base amount of $20 because only $10 of it is figured at the 7% rate. I need to know if there is a way to get the base amount om this scenario? Any help would be greatly appreciated.
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  2. #2
    Senior Member topher0805's Avatar
    Joined
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    You have $10 that is not taxed. You are adding to that another $10 plus tax.

    So, minus $10 from your end amount of $20.70 to get $10.70.

    Then use your formula:

    \frac {10.70}{1.07} = 10

    So, your original amount was $20.
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