# Math Help - [SOLVED] Find Base Total Amount

1. ## [SOLVED] Find Base Total Amount

I believe this to be algebra problem that I have here, but I'm not positive. I'm not even sure that I can find this value mathematically, but I'm sure someone on this forum could tell me. Here is what I need to know:

If I have a base amount of $30 and a final amount of$30.70. I need to know how much of the base amount has been paid for and how much of the .70 tax was paid for.

Example:

$10 is taxable at 7%$20 is NOT taxable
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$30 Base Total If I have this equation here:$30.70 = $20 + ($10+($10 * 7%)) An individual only pays for$10.50.

How do I find how much of the Base amount is left?
$30 - (Portion of payment that is base amount)=Base Amount Left How do I find how much of the tax total is left? .70 - (Portion f paymen that is tax)=Tax Amount Left 2. I am not sure if I understand your question? Are you saying someone has$30, and there is a 7% tax bracket for the first $10, and 0% on the rest? That gives us $10*0.07 =0.7$ in taxes If the tax bracket is up to$10.50, then taxes are equal to $10.50*0.7 = 0.735$ or 73.5 cents in taxes.

3. Thank you for the quick reply. Let me give you the exact scenario I need this for.

This is for an auction business. A buyer may buy 2 items. One for $20 and another for$10. The auction company only charges tax on the $10. The$20 does not have tax because it is "non taxable".

There is a buyers premium fee if someone pays with a credit card on the "base amount remaining". There is no fee if a buyer uses cash. So if the buyer pays $10.50 in cash, and the rest on the credit card. I need to know how much of the "base amount" is left so that the credit card premium will ONLY be charged on the "base amount remaining". A portion of the amount paid will pay for a portion of the .70 in tax and the other portion will pay for some of the base amount. I need to know what those portions are so the credit card premium is only figured on the base amount remaining and not the remaining tax. Let me know if I can elaborate more on this. 4. Let me simply this. 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?

I am opening a new thread. One that isn't so confusing.